fem. proper name, alteration of Sarah (cf. Hal from Harry, Moll from Mary, etc.). Sally Lunn cakes (1780) supposedly named for the woman in Bath who first made them. Sally Ann as a nickname for Salvation Army is recorded from 1927.
1540s (n.), 1550 (v.), from Middle French saillie "a rushing forth," noun use of fem. past participle of saillir "to leap," from Latin salire "to leap" (see salient). Related: Sallied; sallying.