battalion vs army unit

battalion and army unit both are nouns.

Word	Noun	Adjective	Verb	Adverb
battalion	Yes	No	No	No
army unit	Yes	No	No	No

As nouns, army unit is a hypernym of battalion; that is, army unit is a word with a broader meaning than battalion:

battalion: an army unit usually consisting of a headquarters and three or more companies
army unit: a military unit that is part of an army

battalion (noun)	army unit (noun)
an army unit usually consisting of a headquarters and three or more companies	a military unit that is part of an army
a large indefinite quantity