eccentric vs fruitcake

eccentric and fruitcake both are nouns.

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

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

Other hyponyms of eccentric include crackpot, crank, nut, nut case, screwball, nutter, wacko, whacko.

eccentric (noun)	fruitcake (noun)
a person with an unusual or odd personality	a rich cake containing dried fruit and nuts and citrus peel and so on
a person of a specified kind (usually with many eccentricities)	a whimsically eccentric person

eccentric (adjective)	fruitcake (adjective)
not having a common center; not concentric
conspicuously or grossly unconventional or unusual