Order vs ostiary

Order and ostiary both are nouns.

Word	Noun	Adjective	Verb	Adverb
Order	Yes	No	No	No
ostiary	Yes	No	No	No

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

Order: (usually plural) the status or rank or office of a Christian clergyman in an ecclesiastical hierarchy
ostiary: the lowest of the minor Holy Orders in the unreformed Western Church but now suppressed by the Roman Catholic Church

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

Order (noun)	ostiary (noun)
(usually plural) the status or rank or office of a Christian clergyman in an ecclesiastical hierarchy	someone who guards an entrance
	the lowest of the minor Holy Orders in the unreformed Western Church but now suppressed by the Roman Catholic Church