Ancient galley (7)
'ancient galley' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for trireme that I've seen before include "Galley with three banks of oars" , "Ancient vessel with three banks of oars on each side" , "Greek warship" , "Ancient Greek or Roman war galley" , "Ancient galley with three tiers of oars on each side" .)
'ancient galley' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for bireme that I've seen before include "rowing boat" , "ancient craft" , "Ancient galley with two banks of oars on each side" , "Ancient rowed warship" , "old vessel?" .)