semilunar Syllabification: (sem·i·lu·nar)Pronunciation: /ˌsemēˈlo͞onər, ˌsemˌī-/Definition of semilunar adjective chiefly Anatomy shaped like a half-moon or crescent. Origin: late Middle English: from medieval Latin semilunaris (see semi-, lunar)semilunar in other Oxford dictionaries Definition of semilunar in the British & World English dictionary