From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
[1913 Webster]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Tetrarch \Te"trarch\, a.
Four. [Obs.] --Fuller.
[1913 Webster]