trireme

from WordNet (r) 3.0 (2006)

trireme
    n 1: ancient Greek or Roman galley or warship having three tiers
         of oars on each side

from 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]