As nouns the difference between tetrarch and ethnarch
is that tetrarch is a governor of part of a country, especially of a fourth part of a province in Ancient Rome while ethnarch is the governor of a province or people.
tetrarch
English
Noun
(
wikipedia tetrarch)
(
en noun)
a governor of part of a country, especially of a fourth part of a province in Ancient Rome
an officer in charge of a fourth part of a phalanx in Ancient Greece
ethnarch
English
Noun
(
en noun)
(historical, Ancient Greece) The governor of a province or people.
* Lew Wallace, Ben-Hur
- In the course of the struggle with the unfortunate ethnarch , the nobles had found it expedient to attach themselves to Rome.