air bubble vs bubble

air bubble and bubble both are nouns.

Word	Noun	Adjective	Verb	Adverb
air bubble	Yes	No	No	No
bubble	Yes	No	Yes	No

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

air bubble (noun)	bubble (noun)
a bubble of air	a dome-shaped covering made of transparent glass or plastic
	an impracticable and illusory idea
	a speculative scheme that depends on unstable factors that the planner cannot control
	a hollow globule of gas (e.g., air or carbon dioxide)

air bubble (verb)	bubble (verb)
	expel gas from the stomach
	form, produce, or emit bubbles
	cause to form bubbles
	rise in bubbles or as if in bubbles
	flow in an irregular current with a bubbling noise