An isogram is a logological

Logology

Logology is the study of recreational linguistics, an activity that encompasses a wide variety of word games and wordplay emphasizing letter patterns...

 term for a word or phrase without a repeating letter. It is also used by some to mean a word or phrase in which each letter appears the same number of times, not necessarily just once.

In the book Language on Vacation: An Olio of Orthographical Oddities, Dmitri Borgmann

Dmitri Borgmann

Dmitri A. Borgmann is an author best known for coining the word logology and for writing Language On Vacation: An Olio of Orthographical Oddities, published in 1965. This book led Ross Eckler and Trip Payne to join the National Puzzlers' League...

 tries to find the longest isogrammic word. The longest one he found was "Dermatoglyphics

Dermatoglyphics

Dermatoglyphics is the scientific study of fingerprints. The term was coined by Dr. Harold Cummins, the father of American fingerprint analysis, even though the process of fingerprint identification had already been in use for several hundred years. All primates have ridged skin...

" at 15 letters. He coins several longer hypothetical words, such as "thumbscrew-japingly" (18 letters, defined as "as if mocking a thumbscrew

Thumbscrew

The thumbscrews or pilliwinks is a torture instrument which was first used in medieval Europe. It is a simple vice, sometimes with protruding studs on the interior surfaces. The victim's thumbs or fingers were placed in the vice and slowly crushed. The thumbscrew was also applied to crush...

") and, with the "uttermost limit in the way of verbal creativeness", "pubvexingfjord-schmaltzy" (23 letters, defined as "as if in the manner of the extreme sentimentalism

Moral sense theory

Moral sense theory is a view in meta-ethics according to which morality is somehow grounded in moral sentiments or emotions...

 generated in some individuals by the sight of a majestic fjord

Fjord

Geologically, a fjord is a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity.-Formation:A fjord is formed when a glacier cuts a U-shaped valley by abrasion of the surrounding bedrock. Glacial melting is accompanied by rebound of Earth's crust as the ice...

, which sentimentalism is annoying to the clientele of an English inn").

In the book Making the Alphabet Dance, Ross Eckler

A. Ross Eckler, Jr.

Albert Ross Eckler, Jr. is a logologist and statistician, the son of statistician A. Ross Eckler. He received a B.A. from Swarthmore College and a Ph.D. in mathematics from Princeton University....

 reports the word "subdermatoglyphic" (17 letters) can be found in Lowell Goldmith's article Chaos: To See a World in a Grain of Sand and a Heaven in a Wild Flower. He also found the name "Melvin Schwarzkopf" (17 letters), a man living in Alton, Illinois

Alton, Illinois

Alton is a city on the Mississippi River in Madison County, Illinois, United States, about north of St. Louis, Missouri. The population was 27,865 at the 2010 census. It is a part of the Metro-East region of the Greater St. Louis metropolitan area in Southern Illinois...

, and proposed the name "Emily Jung Schwartzkopf" (21 letters). In an elaborate story, Eckler talked about a group of scientists who name the unavoidable urge to speak in pangram

Pangram

A pangram , or holoalphabetic sentence, is a sentence using every letter of the alphabet at least once. Pangrams have been used to display typefaces, test equipment, and develop skills in handwriting, calligraphy, and keyboarding...

s the "Hjelmqvist-Gryb-Zock-Pfund-Wax syndrome".

The longest German isogram is "Heizölrückstoßabdämpfung" (heating oil recoil dampening) with 24 letters, closely followed by "Boxkampfjuryschützlinge" (box fight jury fosterlings) and "Zwölftonmusikbücherjagd" (twelve-tone music book chase) with 23 letters.

15 letters

• misconjugatedly
• uncopyrightable
• dermatoglyphics
  Dermatoglyphics
  Dermatoglyphics is the scientific study of fingerprints. The term was coined by Dr. Harold Cummins, the father of American fingerprint analysis, even though the process of fingerprint identification had already been in use for several hundred years. All primates have ridged skin...
  
  
• hydropneumatics

14 letters

• ambidextrously
• computerizably
• dermatoglyphic
• undiscoverably
• hydropneumatic
• troublemakings

13 letters

• consumptively
• copyrightable
• documentarily
• draughtswomen
• endolymphatic
• flamethrowing
• flowchartings
• hydromagnetic
• metalworkings
• multibranched
• subordinately
• troublemaking
• unmaledictory
• unpredictably
• unproblematic
• unscreamingly
• unsympathized

12 letters

• adsorptively
• ambidextrous
• bankruptcies
• blastodermic
• bluestocking
• cabinetworks
• centrifugals
• computerniks
• configurated
• considerably
• counterplays
• countervails
• customizable
• demonstrably
• discountable
• discrepantly
• disreputably
• doublethinks
• drumbeatings
• earthmovings
• exclusionary
• exculpations
• expurgations
• exhaustingly
• farsightedly
• flexographic
• flowcharting
• Francophiles
• gourmandizes
• granulocytes
• hematoxylins
• housewarming
• hydromancies
• hypnotizable
• imponderably
• incomputable
• incomputably
• kymographies
• lexicography
  Lexicography
  Lexicography is divided into two related disciplines:*Practical lexicography is the art or craft of compiling, writing and editing dictionaries....
  
  
• Lubavitchers
• malnourished
• mendaciously
• metalworking
• multipronged
• nightwalkers
• outpreaching
• outsparkling
• outspreading
• overhaulings
• overmatching
• packinghouse
• pelargoniums
• phagocytized
• phagocytizes
• phytoalexins
• polycentrism
• postcardlike
• problematics
• productively
• questionably
• recognizably
• stakeholding
• stenographic
• stickhandler
• subnormality
• subvocalized
• thunderclaps
• unforgivable
• unglamorized
• unhysterical
• unprofitable
• unprofitably
• upholstering
• voluntaryism
• xylographies

11 letters

• abolishment
• atmospheric
• backgrounds
• campgrounds
• complainers
• copyrighted
• countryside
• dangerously
• disgraceful
• disturbance
• documentary
• facetiously
• filmography
  Filmography
  Filmography is a collective noun for a list of films related by some criterion. For example, an actor's career filmography is the list of films he or she has appeared in; a director's comedy filmography is the list of comedy films directed by a particular director...
  
  
• fluoridates
• lumberjacks
• misanthrope
• misanthropy
• nefariously
• palindrome
  Palindrome
  A palindrome is a word, phrase, number, or other sequence of units that can be read the same way in either direction, with general allowances for adjustments to punctuation and word dividers....
  
  s
• personality
• playgrounds
• playwrights
• precautions
• predictably
• problematic
• republicans
  Republican Party (United States)
  The Republican Party is one of the two major contemporary political parties in the United States, along with the Democratic Party. Founded by anti-slavery expansion activists in 1854, it is often called the GOP . The party's platform generally reflects American conservatism in the U.S...
  
  
• speculation
• stenography
• Switzerland
  Switzerland
  Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
  
  
• thunderclap
• trampoline
  Trampoline
  A trampoline is a device consisting of a piece of taut, strong fabric stretched over a steel frame using many coiled springs. People bounce on trampolines for recreational and competitive purposes....
  
  s
• undesirably
• vouchsafing
• workmanship

10 letters

• aftershock
  Aftershock
  An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...
  
  
• artichoke
  Artichoke
  -Plants:* Globe artichoke, a partially edible perennial thistle originating in southern Europe around the Mediterranean* Jerusalem artichoke, a species of sunflower with an edible tuber...
  
  s
• authorizes
• bankruptcy
• binoculars
  Binoculars
  Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects...
  
  
• blacksmith
  Blacksmith
  A blacksmith is a person who creates objects from wrought iron or steel by forging the metal; that is, by using tools to hammer, bend, and cut...
  
  
• boyfriends
• campground
• clothespin
• complaints
• conjugated
• despicably
• destroying
• downstream
• dumbwaiter
• duplicates
• farsighted
• formidable
• graciously
• hospitable
• infamously
• introduces
• judgmental
• juxtaposed
• lawrencium
  Lawrencium
  Lawrencium is a radioactive synthetic chemical element with the symbol Lr and atomic number 103. In the periodic table of the elements, it is a period 7 d-block element and the last element of actinide series...
  
  
• lumberjack
• malnourish
• mistakenly
• monarchist
• noticeably
• pathfinder
• phlegmatic
• quadriceps
• Scunthorpe
  Scunthorpe
  Scunthorpe is a town within North Lincolnshire, England. It is the administrative centre of the North Lincolnshire unitary authority, and had an estimated total resident population of 72,514 in 2010. A predominantly industrial town, Scunthorpe, the United Kingdom's largest steel processing centre,...
  
  
• shockingly
• slumbering
• trampoline
  Trampoline
  A trampoline is a device consisting of a piece of taut, strong fabric stretched over a steel frame using many coiled springs. People bounce on trampolines for recreational and competitive purposes....
  
  
• trapezoid
  Trapezoid
  In Euclidean geometry, a convex quadrilateral with one pair of parallel sides is referred to as a trapezoid in American English and as a trapezium in English outside North America. A trapezoid with vertices ABCD is denoted...
  
  s
• Volkswagen
  Volkswagen
  Volkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is...
  
  
• waveringly

Isograms are especially useful in the game of Hangman

Hangman (game)

Hangman is a paper and pencil guessing game for two or more players. One player thinks of a word and the other tries to guess it by suggesting letters.-Overview:...

, or would make a particularly difficult puzzle on the game show Wheel of Fortune.