get together vs unite

get together is a noun but unite is not a noun.

Word	Noun	Adjective	Verb	Adverb
get together	Yes	No	Yes	No
unite	No	No	Yes	No

As verbs, unite is a hyponym of get together; that is, unite is a word with a more specific, narrower meaning than get together:

get together (noun)	unite (noun)
a small informal social gathering

get together (verb)	unite (verb)
get together socially or for a specific purpose	become one
become part of; become a member of a group or organization	join or combine
get people together	act in concert or unite in a common purpose or belief
	bring together for a common purpose or action or ideology or in a shared situation
	have or possess in combination
	be or become joined or united or linked