Si, si, or SI may refer to (all SI unless otherwise stated):

Measurement, mathematics and science

  • International System of Units
    International System of Units
    The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

     (Système international d'unités), the modern international standard version of the metric system
  • Signal integrity
    Signal integrity
    Signal integrity or SI is a set of measures of the quality of an electrical signal. In digital electronics, a stream of binary values is represented by a voltage waveform. However, digital signals are fundamentally analog in nature, and all signals are subject to effects such as noise,...

    , electronic circuit tools and techniques that ensure electrical signals are of sufficient quality for proper operation
  • Si, the chemical symbol for silicon
    Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

  • Si(x), the sine integral in mathematics
  • Survey of India
    Survey of India
    The Survey of India is India's central engineering agency in charge of mapping and surveying. Set up in 1767 to help consolidate the territories of the British East India Company, it is one of the oldest Engineering Departments of the Government of India...

    , an Indian government agency responsible for managing geographical information about India
  • Simple Interest (Mathematics)


  • Sacroiliac, an anatomical abbreviation for the sacroiliac (joint)
  • Self-injury
  • Sensory integration
    Sensory integration
    Sensory integration is defined as the neurological process that organizes sensation from one’s own body and the environment, thus making it possible to use the body effectively within the environment. Specifically, it deals with how the brain processes multiple sensory modality inputs into usable...

    , the neurological process that organizes sensation from one's own body and the environment
    • Upper often referring to Primary somatosensory cortex
  • Sexual intercourse
    Sexual intercourse
    Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...

    , a medical abbreviation
  • Suicidal ideation
    Suicidal ideation
    Suicidal ideation is a common medical term for thoughts about suicide, which may be as detailed as a formulated plan, without the suicidal act itself. Although most people who undergo suicidal ideation do not commit suicide, some go on to make suicide attempts...

    , a medical term for thoughts about suicide
  • Structural Integration, a form of bodywork, coined by Dr Ida Rolf


  • Mount Si
    Mount Si
    Mount Si is a mountain in the U.S. state of Washington. It lies on the western margin of the Cascade Range just above the coastal plains around Puget Sound, and towers over the nearby town of North Bend. The mountain was named after local homesteader Josiah "Uncle Si" Merritt...

    , a mountain in state of Washington
  • Si County
    Si County
    Si County is a county of Anhui Province, China. It is under the administration of Suzhou city....

    , county in Anhui, China
  • Si River
    Si River
    The Si River is a watercourse located in Shandong Province, China. It rises in the southern foothills of the Mengshan Mountains then flows through Sishui County, and the cities of Qufu and Yanzhou before emptying into Lake Nanyang...

    , a river in China
  • Slovenia
    Slovenia , officially the Republic of Slovenia , is a country in Central and Southeastern Europe touching the Alps and bordering the Mediterranean. Slovenia borders Italy to the west, Croatia to the south and east, Hungary to the northeast, and Austria to the north, and also has a small portion of...

    , a European nation (esp. internet domain suffix and two-letter abbreviation)
  • Solomon Islands
    Solomon Islands
    Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...

    , a Pacific island nation
  • South India
    South India
    South India is the area encompassing India's states of Andhra Pradesh, Karnataka, Kerala and Tamil Nadu as well as the union territories of Lakshadweep and Pondicherry, occupying 19.31% of India's area...

    , a region in India
  • Southern Ireland
    Southern Ireland
    Southern Ireland was a short-lived autonomous region of the United Kingdom established on 3 May 1921 and dissolved on 6 December 1922.Southern Ireland was established under the Government of Ireland Act 1920 together with its sister region, Northern Ireland...

    , a former constituent country of the UK now officially known as the Republic of Ireland
  • Staten Island
    Staten Island
    Staten Island is a borough of New York City, New York, United States, located in the southwest part of the city. Staten Island is separated from New Jersey by the Arthur Kill and the Kill Van Kull, and from the rest of New York by New York Bay...

    , a borough of New York City and an island in the Hudson River
  • Province of Siena
    Province of Siena
    The Province of Siena is a province in the Tuscany region of Italy. Its capital is the city of Siena.It has an area of 3,821 km² , and a total population of 252,288 . There are 36 comuni in the province...

    , an Italian province (two letter provincial designator)


  • ISO 639 alpha-2 code for the Sinhalese language
  • Si 

Computer science

  • .si
    .si is the Internet country code top-level domain for Slovenia. It is administered by the ARNES, the Academic and Research Network of Slovenia. The registry has reached 80,000 domain names on 19. May 2010-External links:* * *...

    , the Internet country code top-level domain for Slovenia
  • Systems integrator, an IT company that specializes in integrating complex computer or data systems from multiple vendors
  • Shift In, a control code in the C0 control code set
  • Swarm Intelligence
    Swarm intelligence
    Swarm intelligence is the collective behaviour of decentralized, self-organized systems, natural or artificial. The concept is employed in work on artificial intelligence...

    , an artificial intelligence technique
  • Synthetic intelligence
    Synthetic intelligence
    Synthetic intelligence is an alternative term for artificial intelligence which emphasizes that the intelligence of machines need not be an imitation or any way artificial; it can be a genuine form of intelligence. John Haugeland proposes an analogy with artificial and synthetic diamonds—only the...

    , an alternate term for or form of artificial intelligence
  • Silicon Image Inc.
    Silicon Image Inc.
    Silicon Image is a provider of wireless and wired connectivity solutions that enable the reliable distribution and presentation of high-definition content for consumer electronics, mobile, and PC markets...

    , a chip vendor
  • SI register, or source index, in X86 computer architecture


  • Saint Ignatius College Preparatory, a Jesuit college in the United States
  • Samahang Ilokano
    Samahang Ilokano
    The Confederation of Ilocano Association, Incorporated, Samahang Ilokano or Samahang Ilokano is a fraternity and sorority composed of students from colleges and universities in the northern part of the Philippines...

    , a fraternity/sorority based in the Philippines
  • Seletar Institute
    Seletar Institute
    Seletar Institute was one of the four original centralised institutes in Singapore and one of the pre-university centres in Singapore that offers a three-year curriculum leading to the Singapore Cambridge General Certificate of Education Advanced Level examination.-History:SI was established as...

    , a defunct centralised institute in Singapore
  • Silay Institute, Inc., a private college in the Philippines
  • Smithsonian Institution
    Smithsonian Institution
    The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...

    , an American educational and research institute
  • Supplemental Instruction
    Supplemental Instruction
    Overview=Supplemental Instruction is an academic support model developed by Dr. Deanna Martin] at the in 1973 that uses peer-assisted study sessions to improve student and success within targeted historically difficult courses.] The SI program provides by having students who succeeded in...

    , an academic support program often used in higher education


  • Si, a self-replicating artifact in the computer game Ancient Domains of Mystery
    Ancient Domains of Mystery
    Ancient Domains of Mystery, or ADOM, is a roguelike game by Thomas Biskup first released in . The player's aim is to stop the forces of Chaos that invade the world of Ancardia....

  • The Elder Scrolls IV: Shivering Isles
    The Elder Scrolls IV: Shivering Isles
    The Elder Scrolls IV: Shivering Isles is the largest official expansion pack for the role-playing game The Elder Scrolls IV: Oblivion. Announced on January 18, , the expansion was developed, published, and released over the Xbox Live Marketplace by Bethesda Softworks; its retail release was...

    , an expansion pack for The Elder Scrolls IV: Oblivion
  • Sports Interactive
    Sports Interactive
    Sports Interactive Limited is a computer games development company currently based in Old Street, Central London and owned by the Japanese software and video game company Sega. It is the developer of the popular games Football Manager, NHL Eastside Hockey Manager and Championship Manager Quiz, and...

    , a British computer games development company


  • Si, the original name of the seventh note of solfege
    In music, solfège is a pedagogical solmization technique for the teaching of sight-singing in which each note of the score is sung to a special syllable, called a solfège syllable...

    , later changed to "Ti"
  • Sì (song)
    Sì (song)
    "Sì" is the name of the Italian entry to the Eurovision Song Contest 1974, which finished second behind the Swedish entry "Waterloo" sung by ABBA.-Background:...

    , the name of the Italian entry to the Eurovision Song Contest 1974
  • Sì (Carmen Russo song), the name of the 1985 song released by Italian actress Carmen Russo
    Carmen Russo
    Carmen Russo is an Italian dancer, actress, television personality and singer.Russo started her career as a model in the mid 1970s participating in several beauty contests in Italy...

  • (album), an album by Mexican singer and songwriter Julieta Venegas
  • Si, another name for the Sídhe
    The aos sí are a supernatural race in Irish mythology and Scottish mythology are comparable to the fairies or elves. They are said to live underground in the fairy mounds, across the western sea, or in an invisible world that coexists with the world of humans...

    , Celtic mythological beings

Government and politics

  • Catalan Solidarity for Independence, an independist Catalan political party
  • Situationist International, a left-wing organisation
  • Socialist International
    Socialist International
    The Socialist International is a worldwide organization of democratic socialist, social democratic and labour political parties. It was formed in 1951.- History :...

    , a worldwide organization of democratic socialist and labour political parties
  • Sub-Inspector
    Sub-inspector is a rank used extensively in the Indian Police, Pakistani Police and Sri Lankan Police, which is primarily based on the British model. It was formerly used in most British colonial police forces and in certain British police forces as well...

    , a rank in Indian Police forces
  • Survival International
    Survival International
    Survival International is a human rights organisation formed in 1969 that campaigns for the rights of indigenous tribal peoples and uncontacted peoples, seeking to help them to determine their own future. Their campaigns generally focus on tribal peoples' fight to keep their ancestral lands,...

    , a non-governmental indigenous rights organization
  • Station Inspector
    Station Inspector
    Station Inspector is the third highest non-commissioned officer rank in the Singapore Police Force, below that of Senior Station Inspector....

    , the highest non-commissioned rank in the Singapore Police Force
  • Statutory Instrument
    Statutory Instrument
    A Statutory Instrument is the principal form in which delegated or secondary legislation is made in Great Britain.Statutory Instruments are governed by the Statutory Instruments Act 1946. They replaced Statutory Rules and Orders, made under the Rules Publication Act 1893, in 1948.Most delegated...

    , a form of delegated or secondary legislation in Great Britain
  • Swedish Institute
    Swedish Institute
    The Swedish Institute is a Swedish government agency with the responsibility to spread information about Sweden outside of Sweden. It exists to promote Swedish interests, and to organise exchanges with other countries in different areas of public life, in particular in the spheres of culture,...

     (Svenska institutet), a Swedish government agency which promotes Sweden abroad
  • Sí or Solidarity and Equality
    Solidarity and Equality
    Solidarity and Equality is a centre-left Argentine political party, founded in 2008 as a splinter from ARI....

    , an Argentine political party
  • Sitara-i-Imtiaz
    The Sitara-i-Imtiaz , is the third highest honour and civilian award in the State of Pakistan. It recognizes the individuals who made an "especially meritorious contribution to the security or national interests of Pakistan, world peace, cultural or other significant public endeavors"...

    , an honorary award for civilians and the military in Pakistan
  • Societas Iesu
    Society of Jesus
    The Society of Jesus is a Catholic male religious order that follows the teachings of the Catholic Church. The members are called Jesuits, and are also known colloquially as "God's Army" and as "The Company," these being references to founder Ignatius of Loyola's military background and a...

    , the Jesuits, a religious order of the Roman Catholic Church


  • SÍ Sørvágur, a Faroese sports association
  • Sports Illustrated
    Sports Illustrated
    Sports Illustrated is an American sports media company owned by media conglomerate Time Warner. Its self titled magazine has over 3.5 million subscribers and is read by 23 million adults each week, including over 18 million men. It was the first magazine with circulation over one million to win the...

    , an American sports magazine


  • IATA code for Skynet Airlines
    Skynet Airlines
    Skynet Airlines began operations from Shannon International Airport, Ireland, to Amsterdam, Netherlands, with onward connections to Moscow, Russia, using Boeing 737 aircraft...

  • Reporting mark of Spokane International Railroad
    Spokane International Railroad
    The Spokane International Railroad was a short line railroad between Spokane, Washington and the Canadian Pacific Railway at Kingsgate, British Columbia...

    , a former railway in Washington, USA
  • Spark-ignition engine
  • Honda Civic Si
    Honda Civic Si
    The Honda Civic Si is a sport compact / hot hatch version of the Civic built by the Japanese automaker Honda. The Si trim, which stands for "Sport Injected," was introduced for the third generation of Honda Civics in both Japan and North America...


  • Sí (Peruvian magazine)
    Sí (Peruvian magazine)
    Sí is a Peruvian news magazine. In 1993, its editor Ricardo Uceda was instrumental in exposing the La Cantuta Massacre, an incident in which nine students and one professor from La Cantuta University were executed by army soldiers and buried in a mass grave....

    , a magazine notable for its anti-corruption reporting
  • Si (surname) (姒), a Chinese surname used by kings in the Xia Dynasty
    Xia Dynasty
    The Xia Dynasty is the first dynasty in China to be described in ancient historical chronicles such as Bamboo Annals, Classic of History and Records of the Grand Historian. The Xia Dynasty was established by the legendary Yu the Great after Shun, the last of the Five Emperors gave his throne to him...

  • Sergeant Instructor, an appointment in the British Army
  • Scouting Ireland
    Scouting Ireland
    Scouting Ireland is the World Organization of the Scout Movement-recognised Scouting association in the Republic of Ireland, although it also has Scout Groups in Northern Ireland. Scouting Ireland is a voluntary, non-formal educational movement for young people...

    , the national Scouting association of Ireland
  • System integrator
    System integrator
    A systems integrator is a person or company that specializes in bringing together component subsystems into a whole and ensuring that those subsystems function together, a practice known as System Integration...

    , a person or company that specializes in integrating systems
  • Superintendent (police)
    Superintendent (police)
    Superintendent , often shortened to "super", is a rank in British police services and in most English-speaking Commonwealth nations. In many Commonwealth countries the full version is superintendent of police...

    , senior rank of British Police
  • Poetry (film)
    Poetry (film)
    Poetry is a 2010 South Korean drama film written and directed by Lee Chang-dong. It tells the story of a suburban woman in her 60s who begins to grow an interest for poetry while struggling with Alzheimer's disease and her irresponsible grandson. Yoon Jeong-hee stars in the leading role, which was...

    , a 2010 South Korean film with the original title Si (시)
  • Short for the name Simon
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