The Collaborative International Dictionary of English v.0.48:
Trireme \Tri"reme\, n. [L. triremis; tri- (see Tri-) + remus an oar, akin to E. row. See Row to propel with an oar.] (Class. Antiq.) An ancient galley or vessel with tree banks, or tiers, of oars. [1913 Webster]WordNet (r) 3.0 (2006):
trireme n 1: ancient Greek or Roman galley or warship having three tiers of oars on each side