upper side vs crest

upper side and crest both are nouns.

Word	Noun	Adjective	Verb	Adverb
upper side	Yes	No	No	No
crest	Yes	No	Yes	No

As nouns, crest is a hyponym of upper side; that is, crest is a word with a more specific, narrower meaning than upper side:

Other hyponyms of upper side include crown, poll, crown, pate, poll, desktop, rooftop, tiptop.

upper side (noun)	crest (noun)
the highest or uppermost side of anything	a showy growth of e.g. feathers or skin on the head of a bird or other animal
	(heraldry) in medieval times, an emblem used to decorate a helmet
	the center of a cambered road
	the top line of a hill, mountain, or wave
	the top or extreme point of something (usually a mountain or hill)

upper side (verb)	crest (verb)
	reach a high point
	lie at the top of