voyeur vs viewer

voyeur and viewer both are nouns.

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

As nouns, viewer is a hypernym of voyeur; that is, viewer is a word with a broader meaning than voyeur:

voyeur: a viewer who enjoys seeing the sex acts or sex organs of others
viewer: a close observer; someone who looks at something (such as an exhibition of some kind)

Other hypernyms of voyeur include looker, spectator, watcher, witness.

voyeur (noun)	viewer (noun)
a viewer who enjoys seeing the sex acts or sex organs of others	an optical device for viewing photographic transparencies
	a close observer; someone who looks at something (such as an exhibition of some kind)