What's the difference between tetrarch and tetrarchy?

Tetrarch

Definition:

• (a.) A Roman governor of the fourth part of a province; hence, any subordinate or dependent prince; also, a petty king or sovereign.
• (a.) Four.

Example Sentences:

Tetrarchy

Definition:

• (n.) The district under a Roman tetrarch; the office or jurisdiction of a tetrarch; a tetrarchate.

Example Sentences: