ONSIDE Meaning of ONSIDE in English on ‧ side /ˌɒnˈsaɪd◂ $ ˌɑːn-, ˌɒːn-/ BrE AmE adjective , adverb in a position where you are allowed to play the ball in sports such as football OPP offside Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012