motormouth vs talker

motormouth and talker both are nouns.

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

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

motormouth: someone who talks incessantly
talker: 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, utterer, verbaliser, verbalizer.

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