blabber vs utter

blabber is a noun but utter is not a noun.

Word	Noun	Adjective	Verb	Adverb
blabber	Yes	No	Yes	No
utter	No	Yes	Yes	No

As verbs, utter is a hypernym of blabber; that is, utter is a word with a broader meaning than blabber:

Other hypernyms of blabber include mouth, speak, talk, verbalise, verbalize.

blabber (noun)	utter (noun)
one who reveals confidential information to the police or other authority

blabber (adjective)	utter (adjective)
	complete and absolute
	without qualification; used informally as (often pejorative) intensifiers

blabber (verb)	utter (verb)
speak (about unimportant matters) rapidly and incessantly	express in speech
	articulate; either verbally or with a cry, shout, or noise
	express audibly; utter sounds (not necessarily words)
	put into circulation