viewer vs spectator

viewer and spectator both are nouns.

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

As nouns, viewer and spectator are synonyms defined as:

viewer and spectator: a close observer; someone who looks at something (such as an exhibition of some kind)

Other synonyms of viewer include looker, watcher, witness.

viewer (noun)	spectator (noun)
an optical device for viewing photographic transparencies	a woman's pump with medium heel; usually in contrasting colors for toe and heel
a close observer; someone who looks at something (such as an exhibition of some kind)	a close observer; someone who looks at something (such as an exhibition of some kind)