screwball vs fruitcake

screwball and fruitcake both are nouns.

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

As nouns, screwball and fruitcake are synonyms defined as:

Other synonyms of screwball include crackpot, crank, nut, nut case.

screwball (noun)	fruitcake (noun)
a pitch with reverse spin that curves toward the side of the plate from which it was thrown	a rich cake containing dried fruit and nuts and citrus peel and so on
a whimsically eccentric person	a whimsically eccentric person

screwball (adjective)	fruitcake (adjective)
foolish; totally unsound