whisper vs utter

whisper is a noun but utter is not a noun.

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

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

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

whisper (noun)	utter (noun)
speaking softly without vibration of the vocal cords
a light noise, like the noise of silk clothing or leaves blowing in the wind

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

whisper (verb)	utter (verb)
speak softly; in a low voice	express in speech
	articulate; either verbally or with a cry, shout, or noise
	express audibly; utter sounds (not necessarily words)
	put into circulation