yack away vs speak

yack away and speak both are verbs.

Word	Noun	Adjective	Verb	Adverb
yack away	No	No	Yes	No
speak	No	No	Yes	No

As verbs, speak is a hypernym of yack away; that is, speak is a word with a broader meaning than yack away:

Other hypernyms of yack away include mouth, talk, utter, verbalise, verbalize.

yack away (verb)	speak (verb)
talk incessantly and tiresomely	express in speech
	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound