triaconter

from The Century Dictionary.

• noun In Greek antiquity, a vessel of thirty oars.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Gr. Antiq.) A vessel with thirty banks of oars, or, as some say, thirty ranks of rowers.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun historical, Ancient Greece A vessel with thirty banks of oars, or thirty ranks of rowers.