blurt out vs utter

blurt out is not an adjective while utter is an adjective.

Word	Noun	Adjective	Verb	Adverb
blurt out	No	No	Yes	No
utter	No	Yes	Yes	No

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

Other hypernyms of blurt out include mouth, speak, talk, verbalise, verbalize.

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

blurt out (verb)	utter (verb)
utter impulsively	express in speech
	articulate; either verbally or with a cry, shout, or noise
	express audibly; utter sounds (not necessarily words)
	put into circulation