stance vs viewpoint

stance and viewpoint both are nouns.

Word	Noun	Adjective	Verb	Adverb
stance	Yes	No	No	No
viewpoint	Yes	No	No	No

As nouns, viewpoint is a hyponym of stance; that is, viewpoint is a word with a more specific, narrower meaning than stance:

Other hyponyms of stance include hard line, point of view, stand, standpoint.

stance (noun)	viewpoint (noun)
standing posture	a mental position from which things are viewed
a rationalized mental attitude	a place from which something can be viewed