gnaw vs jaw

gnaw is not a noun while jaw is a noun.

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

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

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

gnaw (noun)	jaw (noun)
	holding device consisting of one or both of the opposing parts of a tool that close to hold an object
	the part of the skull of a vertebrate that frames the mouth and holds the teeth
	the bones of the skull that frame the mouth and serve to open it; the bones that hold the teeth

gnaw (verb)	jaw (verb)
become ground down or deteriorate	talk socially without exchanging too much information
bite or chew on with the teeth	censure severely or angrily
	talk incessantly and tiresomely
	chew (food); to bite and grind with the teeth