FILLY Meaning of FILLY in English fil ‧ ly /ˈfɪli/ BrE AmE noun ( plural fillies ) [countable] [ Date: 1400-1500 ; Language: Old Norse ; Origin: fylja ] a young female horse ⇨ colt , foal Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012