fem. proper name, mid-12c., from Old French Agnes, from Greek Hagne "pure, chaste," fem. of hagnos "holy, sacred" (of places); "chaste, pure; guiltless, morally upright" (of persons), from PIE *yag-no-, suffixed form of root *yag- "to worship, reverence" (see hagiology).
St. Agnes, martyred 303 C.E., is patron saint of young girls, hence the folk connection of St. Agnes' Eve (Jan. 20-21) with love divinations. In Middle English, frequently written phonetically as Annis, Annys. In U.S., among the top 50 names for girls born between 1887 and 1919.