Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

trireme
     n : ancient Greek or Roman galley or warship having three tiers
         of oars on each side