gnaw vs chew

gnaw is not a noun while chew is a noun.

Word	Noun	Adjective	Verb	Adverb
gnaw	No	No	Yes	No
chew	Yes	No	Yes	No

As verbs, chew is a hypernym of gnaw; that is, chew is a word with a broader meaning than gnaw:

Other hypernyms of gnaw include jaw, manducate, masticate, bite, seize with teeth.

gnaw (noun)	chew (noun)
	biting and grinding food in your mouth so it becomes soft enough to swallow
	a wad of something chewable as tobacco

gnaw (verb)	chew (verb)
become ground down or deteriorate	chew (food); to bite and grind with the teeth
bite or chew on with the teeth