air unit vs squadron

air unit and squadron both are nouns.

Word	Noun	Adjective	Verb	Adverb
air unit	Yes	No	No	No
squadron	Yes	No	No	No

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

Other hyponyms of air unit include air division, division, wing, air group, flight.

air unit (noun)	squadron (noun)
a military unit that is part of the airforce	an air force unit larger than a flight and smaller than a group
	a cavalry unit consisting of two or more troops and headquarters and supporting arms
	a naval unit that is detached from the fleet for a particular task