adult vs eccentric

adult and eccentric both are nouns.

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

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

adult (noun)	eccentric (noun)
any mature animal	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)

adult (adjective)	eccentric (adjective)
(of animals) fully developed	not having a common center; not concentric
designed to arouse lust	conspicuously or grossly unconventional or unusual