gibber vs utter

gibber is a noun but utter is not a noun.

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

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

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

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

Other hypernyms of gibber include emit, let loose, let out.

gibber (noun)	utter (noun)
unintelligible talking

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

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