Word Origin & History
O.E. sweostor, swuster, or a Scand. cognate (cf. O.N. systir, Swed. sister, Dan. søster), in either case from P.Gmc. *swestr- (cf. O.S. swestar, O.Fris. swester, M.Du. suster, Du. zuster, O.H.G. swester, Ger. Schwester, Goth. swistar), from PIE *swesor, one of the most persistent and unchanging
PIE root words, recognizable in almost every modern I.E. language (cf. Skt. svasar-, Avestan shanhar-, L. soror, O.C.S., Rus. sestra, Lith. sesuo, O.Ir. siur, Welsh chwaer, Gk. eor). Probably from PIE roots *swe- "one's own" + *ser- "woman." For vowel evolution, see bury
. Used of nuns in O.E.; of a woman in general from 1906; of a black woman from 1926; and in the sense of "fellow feminist" from 1912.