oddball vs fruitcake

oddball and fruitcake both are nouns.

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

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

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

oddball (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 whimsically eccentric person