browser vs viewer

browser and viewer both are nouns.

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

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

browser: a viewer who looks around casually without seeking anything in particular
viewer: a close observer; someone who looks at something (such as an exhibition of some kind)

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

browser (noun)	viewer (noun)
a program used to view HTML documents	an optical device for viewing photographic transparencies
a viewer who looks around casually without seeking anything in particular	a close observer; someone who looks at something (such as an exhibition of some kind)