perceiver vs viewer

perceiver and viewer both are nouns.

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

As nouns, viewer is a hyponym of perceiver; that is, viewer is a word with a more specific, narrower meaning than perceiver:

perceiver: a person who becomes aware (of things or events) through the senses
viewer: a close observer; someone who looks at something (such as an exhibition of some kind)

perceiver (noun)	viewer (noun)
a person who becomes aware (of things or events) through the senses	an optical device for viewing photographic transparencies
	a close observer; someone who looks at something (such as an exhibition of some kind)