Source : Webster's Revised Unabridged Dictionary (1913)

Tetrarch \Te"trarch\, n. [L. tetrarches, Gr. ?, ?; te`tra- (see
   {Tetra-}) + ? a ruler, ? to lead; rule: cf. F. t['e]trarque.
   See {Arch}, a.] (Rom. Antiq.)
   A Roman governor of the fourth part of a province; hence, any
   subordinate or dependent prince; also, a petty king or
   sovereign.

Tetrarch \Te"trarch\, a.
   Four. [Obs.] --Fuller.