unite vs join

unite is not a noun while join is a noun.

Word	Noun	Adjective	Verb	Adverb
unite	No	No	Yes	No
join	Yes	No	Yes	No

As verbs, join is a hypernym of unite; that is, join is a word with a broader meaning than unite:

Other hypernyms of unite include fall in, get together.

As verbs, unite and join are synonyms defined as:

Other synonyms of unite include connect, link, link up.

unite (noun)	join (noun)
	a set containing all and only the members of two or more given sets
	the shape or manner in which things come together and a connection is made

unite (verb)	join (verb)
become one	make contact or come together
join or combine	cause to become joined or linked
act in concert or unite in a common purpose or belief	become part of; become a member of a group or organization
bring together for a common purpose or action or ideology or in a shared situation	come into the company of
have or possess in combination	be or become joined or united or linked
be or become joined or united or linked