The Collaborative International Dictionary
Triaconter
Triaconter \Tri"a*con`ter\, n. [Gr. ?, fr. ? thirty.] (Gr. Antiq.) A vessel with thirty banks of oars, or, as some say, thirty ranks of rowers.
Wiktionary
triaconter
n. (context historical Ancient Greece English) A vessel with thirty banks of oars, or thirty ranks of rowers.