witnesser vs perceiver

witnesser and perceiver both are nouns.

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

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

witnesser: someone who sees an event and reports what happened
perceiver: a person who becomes aware (of things or events) through the senses

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

witnesser (noun)	perceiver (noun)
someone who sees an event and reports what happened	a person who becomes aware (of things or events) through the senses