From Middle English sister, suster, from Old English swustor, sweoster, sweostor ("sister, nun"); from Proto-Germanic *swestēr, from Proto-Indo-European *swésōr.

Cognate with Scots sister, syster ("sister"), Western Frisian sus, suster ("sister"), Dutch zuster, German Schwester, Norwegian Bokmål søster, Norwegian Nynorsk - and Swedish syster, Icelandic systir, Gothic 𐍃𐍅𐌹𐍃𐍄𐌰𐍂, Latin soror, Russian сестра́, Lithuanian sesuo, Albanian vajzë, Sanskrit स्वसृ, Persian خواهر.

In standard English, the form with i is due to contamination with Old Norse systir.

The plural sistren is from Middle English sistren, a variant plural of sister, suster; compare brethren.

• (British) IPA: /ˈsɪs.tə(ɹ)/
• (America) enPR: sĭs'tər, IPA: /ˈsɪs.tɚ/

sister (plural sisters)

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

   Synonyms: sis

   Antonyms: brother

   Hypernyms: sibling

   My sister is always driving me crazy.

2. A female member of a religious order; especially one devoted to more active service; (informally) a nun.

   Synonyms: nun

   Coordinate terms: brother, friar, frater

   Michelle left behind her bank job and became a sister at the local convent.

3. Any butterfly in the genus Adelpha, so named for the resemblance of the dark-colored wings to the black habit traditionally worn by nuns.
4. (British) A senior or supervisory nurse, often in a hospital.

   Synonyms: charge nurse

5. Any woman or girl with whom a bond is felt through the same biological sex, gender or common membership in a community, race, profession, religion, organization, or ism.

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

6. (AAVE, slang, sometimes, capitalized) A black woman.
   • 2006, Noire [pseudonym], Thug-A-Licious: An Urban Erotic Tale, New York, N.Y.: One World, Ballantine Books, →ISBN, page 169 ↗:

     A fly sister rolled in with a suitcase full of hip-hop novels called The Glamorous Life, and an African brother with long dreads wanted to sell them some incense and some fake Jacob watches.

   • 2014, J. L. King, Full Circle: Loving. Living. Life. After The Down Low:

     And now, social media has made it worse. From Facebook to Twitter, I get all kinds of invitations. Recently a sister inboxed me on Facebook and told me that she knew for a fact that I wanted her and she wanted me.

7. (informal) A form of address to a woman.

   Synonyms: darling, dear, love, lady, miss, pet

   What’s up, sister?

8. A woman, in certain religious, labour or socialist circles; also as a form of address.

   Thank you, sister. I would like to thank the sister who just spoke.

9. (attributively) An entity that has a special or affectionate, non-hierarchical relationship with another.

   Synonyms: affiliate, affiliated

   sister publication

   sister city

   sister projects

10. (comptheory) A node in a data structure that shares its parent with another node.
11. (usually, attributively) Something in the same class.

    sister ships

    sister facility

• sororal
• sistren
• suster
• sustah

see sister/translations

sister (sisters, present participle sistering; simple past and past participle sistered)

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

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

2. (obsolete, transitive) To be sister to; to resemble closely.
   • c. 1607–1608, William Shakeſpeare, The Late, And much admired Play, Called Pericles, Prince of Tyre. […], London: Imprinted at London for Henry Goſſon,  […], published 1609, →OCLC ↗, [Act V, scene 1] ↗:

     Deep clerks she dumbs; and with her needle composes
     Nature's own shape, of bud, bird, branch, or berry,
     That even her art sisters the natural roses;
     Her inkle, silk, twin with the rubied cherry

• German: aufdoppeln, verstärken

sister (plural sisters)

1. Title of respect for an adult female member of a religious order.

   At the convent, Sister Grace supervises the kitchen.

   Please welcome Sister Smith as she moves from her former congregation to her new congregation.

   Could you say a prayer for me, Sister?

2. Title of respect for an adult female member of a fraternal/sororal organization, or comrade in a movement, or even a stranger using fictive kin.
   • 1983, Official Proceedings, Resolutions, Constitution and Merger Agreement of the United Food and Commercial Workers International Union Convention:

     Sister Huerta was to have been our initial speaker this morning. However, we received word later this morning that Sister Huerta would be unable to attend our convention.

3. A title used to personify or respectfully refer to concepts or animals.

   Native American leader Chief Seattle urged ecological responsibility, referring to Brother Eagle and Sister Sky in his purported 1854 speech.

• Ss.
• Sis.
• Sr.

• sister
• sisterhood
• Sisterhood
• sistren
• Sistren