The Collaborative International Dictionary of English v.0.48:

Navarch \Na"varch\ (n[=a]"v[aum]rk), n. [L. navarchus, Gr.
   nay`archo`s; nay^s ship + 'archo`s chief.] (Gr. Antiq.)
   The commander of a fleet. --Mitford.
   [1913 Webster]