chew vs gnaw

chew is a noun but gnaw is not a noun.

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

As verbs, gnaw is a hyponym of chew; that is, gnaw is a word with a more specific, narrower meaning than chew:

Other hyponyms of chew include champ, chomp, champ, gum, mumble, chaw, crunch, munch.

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

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