drone on vs utter

drone on is not an adjective while utter is an adjective.

Word	Noun	Adjective	Verb	Adverb
drone on	No	No	Yes	No
utter	No	Yes	Yes	No

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

Other hypernyms of drone on include mouth, speak, talk, verbalise, verbalize.

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

drone on (verb)	utter (verb)
talk in a monotonous voice	express in speech
	articulate; either verbally or with a cry, shout, or noise
	express audibly; utter sounds (not necessarily words)
	put into circulation