pair vs conjoin

pair is a noun but conjoin is not a noun.

Word	Noun	Adjective	Verb	Adverb
pair	Yes	No	Yes	No
conjoin	No	No	Yes	No

As verbs, conjoin is a hypernym of pair; that is, conjoin is a word with a broader meaning than pair:

Other hypernyms of pair include join.

pair (noun)	conjoin (noun)
two people considered as a unit
a set of two similar things considered as a unit
a poker hand with 2 cards of the same value
two items of the same kind

pair (verb)	conjoin (verb)
engage in sexual intercourse	make contact or come together
bring two objects, ideas, or people together	take in marriage; married
arrange in pairs
occur in pairs
form a pair or pairs