theatergoer vs viewer

theatergoer and viewer both are nouns.

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

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

theatergoer: someone who attends the theater
viewer: a close observer; someone who looks at something (such as an exhibition of some kind)

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

theatergoer (noun)	viewer (noun)
someone who attends the theater	an optical device for viewing photographic transparencies
	a close observer; someone who looks at something (such as an exhibition of some kind)