witnesser vs observer

witnesser and observer both are nouns.

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

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

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

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

witnesser (noun)	observer (noun)
someone who sees an event and reports what happened	a person who becomes aware (of things or events) through the senses
	an expert who observes and comments on something