A young female horse, especially a racehorse less than five years old, or a young female of another equine species.
A young female horse, specif. one under five years of age.
A lively, high-spirited girl or young woman.
A vivacious young woman or girl.
(dated) A young attractive female.
Hey, Homer, get a load of the gams on that filly!
Origin of filly
Middle English filli from Old Norse fylja pau-1 in Indo-European roots