air unit vs air group

air unit and air group both are nouns.

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

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

air unit: a military unit that is part of the airforce
air group: a unit of the United States Air Force larger than a squadron and smaller than a wing

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

air unit (noun)	air group (noun)
a military unit that is part of the airforce	a unit of the United States Air Force larger than a squadron and smaller than a wing