FILLY Meaning of FILLY in English n. (pl. -ies) 1 a young female horse, usu. before it is four years old. 2 colloq. a girl or young woman. [ ME, prob. f. ON fylja f. Gmc (as FOAL) ] Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012