[sis.ter] n [ME suster, sister, partly fr. OE sweostor and partly of Scand origin; akin to ON systir sister; akin to L soror sister, Skt svasr] (bef. 12c) 1: a female who has one or both parents in common with another
2. often cap a: a member of a women's religious order (as of nuns or deaconesses); esp: one of a Roman Catholic congregation under simple vows b: a woman or girl who is a member of a Christian church
3: a woman regarded as a comrade "my Korean ~s --Alice Walker"
4: one that is closely similar to or associated with another "~ schools" "~ cities"
5. chiefly Brit: nurse
6. a: girl, woman; esp: a girl or woman who is black b: person--usu. used in the phrase weak sister 7: a member of a sorority