Order vs ostiarius

Order and ostiarius both are nouns.

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

As nouns, ostiarius is a hyponym of Order; that is, ostiarius 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
ostiarius: 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, ostiary, exorcist, lector, reader, priest, subdeacon.

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