Entry 1 sense Webster, 1913 Apennine /ăp'-ən-ēnˌ/ · Ap·en·nine · IPA /ˈæpənaɪn/ 01 a. Of, pertaining to, or designating, the Apennines, a chain of mountains extending through Italy. 1. Of, pertaining to, or designating, the Apennines, a chain of mountains extending through Italy.