Etymology

suster from systir and , both from , from .

Germanic cognates: Old Frisian swester, Old Saxon swestar (Dutch zuster), Old High German swester (German Schwester), Gothic 𐍃𐍅𐌹𐍃𐍄𐌰𐍂.

Indo-European cognates: Latin soror, Old Irish siur (Welsh chwaer), Old Church Slavonic сестра (Russian сестра), Lithuanian sesuõ.

Noun

1. a daughter of the same parents as another person; a female sibling.

   My little sister is an annoying pest.

2. a female member of a religious community; a nun.
3. a senior or supervisory nurse, often in a hospital.
4. any woman or girl with whom a bond is felt through common membership of a race, profession, religion or organization, such as feminism.

   Connie was very close to her friend Judy and considered her to be her sister.

   • 1985, Eurythmics and Aretha Franklin, Who’s Zoomin' Who?:

     [song title] Sisters Are Doin’ It for Themselves

5. a black woman
6. a form of address to a woman
   • What’s up, sister?
7. Of or relating to an entity that has a special or affectionate relationship with another

   sister publication

   sister city

Synonyms

sis nun charge nurse darling, dear, lady, love, miss, pet

Verb

1. To strengthen (a supporting beam) by fastening a second beam alongside it.

   I’m trying to correct my sagging floor by sistering the joists.