army unit vs squad

army unit and squad both are nouns.

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

As nouns, squad is a hyponym of army unit; that is, squad is a word with a more specific, narrower meaning than army unit:

army unit (noun)	squad (noun)
a military unit that is part of an army	a cooperative unit (especially in sports)
	a smallest army unit
	a small squad of policemen trained to deal with a particular kind of crime