priest vs high priest

priest and high priest both are nouns.

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

As nouns, high priest is a hyponym of priest; that is, high priest 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
high priest: a senior clergyman and dignitary

priest (noun)	high priest (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 preeminent authority or major proponent of a movement or doctrine