crackpot vs fruitcake

crackpot and fruitcake both are nouns.

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

As nouns, crackpot and fruitcake are synonyms defined as:

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

crackpot (noun)	fruitcake (noun)
a whimsically eccentric person	a rich cake containing dried fruit and nuts and citrus peel and so on
	a whimsically eccentric person