rejuvenescence vs youth

rejuvenescence and youth both are nouns.

Word	Noun	Adjective	Verb	Adverb
rejuvenescence	Yes	No	No	No
youth	Yes	No	No	No

As nouns, youth is a hypernym of rejuvenescence; that is, youth is a word with a broader meaning than rejuvenescence:

Other hypernyms of rejuvenescence include juvenility, youthfulness.

rejuvenescence (noun)	youth (noun)
A renewal of youthful characteristics or vitality.	the freshness and vitality characteristic of a young person
	young people collectively
	a young person (especially a young man or boy)
	early maturity; the state of being young or immature or inexperienced
	the time of life between childhood and maturity
	an early period of development