eccentric vs grownup

eccentric and grownup both are nouns.

Word	Noun	Adjective	Verb	Adverb
eccentric	Yes	Yes	No	No
grownup	Yes	Yes	No	No

As nouns, grownup is a hypernym of eccentric; that is, grownup is a word with a broader meaning than eccentric:

Other hypernyms of eccentric include adult.

eccentric (noun)	grownup (noun)
a person with an unusual or odd personality	a fully developed person from maturity onward
a person of a specified kind (usually with many eccentricities)

eccentric (adjective)	grownup (adjective)
not having a common center; not concentric	(of animals) fully developed
conspicuously or grossly unconventional or unusual