stammerer vs utterer

stammerer and utterer both are nouns.

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

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

stammerer: someone who speaks with involuntary pauses and repetitions
utterer: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

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

stammerer (noun)	utterer (noun)
someone who speaks with involuntary pauses and repetitions	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