peeper vs viewer

peeper and viewer both are nouns.

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

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

peeper: 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 peeper include looker, spectator, watcher, witness.

peeper (noun)	viewer (noun)
an animal that makes short high-pitched sounds	an optical device for viewing photographic transparencies
an informal term referring to the eye	a close observer; someone who looks at something (such as an exhibition of some kind)
a viewer who enjoys seeing the sex acts or sex organs of others