pentecontarch
/pɛntɪˈkɒntɑːk/noun
Ancient History. A person in charge of a fifty-oared ship; the commander of a penteconter.
Origin
Late Middle English (in an earlier sense). From post-classical Latin pentecontarchus commander of fifty (Vetus Latina) from ancient Greek πεντηκόνταρχος commander of fifty (at Athens; also in Septuagint) from πεντήκοντα fifty + -αρχος.