Definition of sister
1
: a female who has one or both parents in common with another
2
often capitalized
a
: a member of a women's religious order (as of nuns or deaconesses);
especially
: one of a Roman Catholic congregation under simple vows
b
: a girl or woman who is a member of a Christian church
3 a
: a girl or woman regarded as a comrade
b
: a girl or woman who shares with another a common national or racial origin;
especially
: a black girl or woman
4
: one that is closely similar to or associated with another
- sister cities
7
: a member of a sorority
