priest vs hierarch

priest and hierarch both are nouns.

Word	Noun	Adjective	Verb	Adverb
priest	Yes	No	No	No
hierarch	Yes	No	No	No

As nouns, hierarch is a hyponym of priest; that is, hierarch is a word with a more specific, narrower meaning than priest:

priest: a clergyman in Christian churches who has the authority to perform or administer various religious rites; one of the Holy Orders
hierarch: a senior clergyman and dignitary

priest (noun)	hierarch (noun)
a clergyman in Christian churches who has the authority to perform or administer various religious rites; one of the Holy Orders	a senior clergyman and dignitary
a person who performs religious duties and ceremonies in a non-Christian religion	a person who holds a high position in a hierarchy