yack vs yak

yack and yak both are nouns.

Word	Noun	Adjective	Verb	Adverb
yack	Yes	No	Yes	No
yak	Yes	No	Yes	No

As nouns, yack and yak are synonyms defined as:

Other synonyms of yack include cackle, chatter, yakety-yak.

yack (noun)	yak (noun)
noisy talk	large long-haired wild ox of Tibet often domesticated
	noisy talk

yack (verb)	yak (verb)
talk incessantly and tiresomely	talk profusely