platoon vs army unit

platoon and army unit both are nouns.

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

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

platoon: a military unit that is a subdivision of a company; usually has a headquarters and two or more squads; usually commanded by a lieutenant
army unit: a military unit that is part of an army

platoon (noun)	army unit (noun)
a military unit that is a subdivision of a company; usually has a headquarters and two or more squads; usually commanded by a lieutenant	a military unit that is part of an army
a team of policemen working under the military platoon system
a group of persons who are engaged in a common activity