air filter vs filter

air filter and filter both are nouns.

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

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

air filter (noun)	filter (noun)
a filter that removes dust from the air that passes through it	device that removes something from whatever passes through it
	an electrical device that alters the frequency spectrum of signals passing through it

air filter (verb)	filter (verb)
	remove by passing through a filter
	pass through
	run or flow slowly, as in drops or in an unsteady stream