gnaw at vs gnaw

gnaw at and gnaw both are verbs.

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

As verbs, gnaw at and gnaw are synonyms defined as:

Other synonyms of gnaw at include eat at, erode, wear away.

gnaw at (verb)	gnaw (verb)
become ground down or deteriorate	become ground down or deteriorate
	bite or chew on with the teeth