The penteconter (alt. spelling pentekonter, pentaconter, pentecontor or pentekontor; Greek: πεντηκόντερος, pentēkónteros, "fifty-oared"), plural penteconters, was an ancient Greek galley in use since the archaic period.
In an alternative meaning, the term was also used for a military commander of fifty men in ancient Greece.
Androsthenes (Ancient Greek: Ἀνδροσθένης; literally meaning: "Man's Strength") of Thasos, son of Callistratus, was one of the admirals of Alexander the Great. He sailed as a trierarch with Nearchus, and was also sent by Alexander down the Euphrates to explore the coast of the Persian Gulf, skirting the coast of Arabia in a triacontor and sailing further than Archias of Pella. He wrote an account of this voyage, titled The Navigation of the Indian sea ('Ὁ τῆς Ἰνδικῆς παραπλοῦς).