Holy Order vs priest

Holy Order and priest both are nouns.

Word	Noun	Adjective	Verb	Adverb
Holy Order	Yes	No	No	No
priest	Yes	No	No	No

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

Holy Order: (usually plural) the status or rank or office of a Christian clergyman in an ecclesiastical hierarchy
priest: a clergyman in Christian churches who has the authority to perform or administer various religious rites; one of the Holy Orders

Other hyponyms of Holy Order include acolyte, anagnost, deacon, doorkeeper, ostiarius, ostiary, exorcist, lector, reader, subdeacon.

Holy Order (noun)	priest (noun)
(usually plural) the status or rank or office of a Christian clergyman in an ecclesiastical hierarchy	a clergyman in Christian churches who has the authority to perform or administer various religious rites; one of the Holy Orders
	a person who performs religious duties and ceremonies in a non-Christian religion