Peeping Tom vs viewer

Peeping Tom and viewer both are nouns.

Word	Noun	Adjective	Verb	Adverb
Peeping Tom	Yes	No	No	No
viewer	Yes	No	No	No

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

Peeping Tom: 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 Peeping Tom include looker, spectator, watcher, witness.

Peeping Tom (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)