blab vs utter

blab is not an adjective while utter is an adjective.

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

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

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

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

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