witnesser vs utterer

witnesser and utterer both are nouns.

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

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

witnesser: someone who sees an event and reports what happened
utterer: someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)

Other hypernyms of witnesser include beholder, observer, perceiver, percipient, speaker, talker, verbaliser, verbalizer.

witnesser (noun)	utterer (noun)
someone who sees an event and reports what happened	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