Entry 1 sense Webster, 1913 Trireme /trīr'-ēmˌ/ · Tri·reme · IPA /ˈtɹaɪ.ɹiːm/ 01 n. An ancient galley or vessel with tree banks, or tiers, of oars. 1. An ancient galley or vessel with tree banks, or tiers, of oars.(Class. Antiq.)