motormouth vs utterer

motormouth and utterer both are nouns.

Word	Noun	Adjective	Verb	Adverb
motormouth	Yes	No	No	No
utterer	Yes	No	No	No

As nouns, utterer is a hypernym of motormouth; that is, utterer is a word with a broader meaning than motormouth:

motormouth: someone who talks incessantly
utterer: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

Other hypernyms of motormouth include speaker, talker, verbaliser, verbalizer.

motormouth (noun)	utterer (noun)
someone who talks incessantly	someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)
	someone who circulates forged banknotes or counterfeit coins
	an organism that can utter vocal sounds