filly
/ˈfɪlɪ/noun
(pl. -ies)
1- a young female horse, especially one less than four years old（尤指四岁以下的）小牝马。
1.1
- dated a lively girl or young woman〈旧〉活泼的姑娘。
词源
late Middle English: from Old Norse fylja, of Germanic origin; related to FOAL.