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.