Meaning of TETRARCH

Gr.: "prince over a quarter."
This term originally designated a person who governed a quarter of a state or province. Philip of Macedon divided Thessaly into four tetrarchies.

Later the title was applied to subordinate princes, although the territory was not divided between four princes. The Romans called tetrarchs a rank of princes lower than kings and ethnarchs.

The NT mentions three:
Herod tetrarch of Galilee,
Philip tetrarch of Iturea and Traconítida, and
Lysanias, tetrarch of Abilinia (Lk. 3:1).

Augustus gave the title of ethnarch and half of Herod the Great's kingdom to Archelaus. The other half he divided into two tetrarchies, which he assigned to Herod Antipas and Philip (Ant. 17:11, 4; Wars 2:6, 3).

Sometimes the title of king was given to the tetrarchs, as a courtesy (Mt. 14:1, cf. v. 9; Mr. 6:14).