air cushion vs compressed air

air cushion and compressed air both are nouns.

Word	Noun	Adjective	Verb	Adverb
air cushion	Yes	No	No	No
compressed air	Yes	No	No	No

As nouns, compressed air is a hypernym of air cushion; that is, compressed air is a word with a broader meaning than air cushion:

air cushion: the trapped air that supports a hovercraft a short distance above the water or ground
compressed air: air at a pressure greater than that of the atmosphere

air cushion (noun)	compressed air (noun)
a cushion usually made of rubber or plastic that can be inflated	air at a pressure greater than that of the atmosphere
a mechanical device using confined air to absorb the shock of motion
the trapped air that supports a hovercraft a short distance above the water or ground