crackpot vs nut case

crackpot and nut case both are nouns.

Word	Noun	Adjective	Verb	Adverb
crackpot	Yes	No	No	No
nut case	Yes	No	No	No

As nouns, crackpot and nut case are synonyms defined as:

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

crackpot (noun)	nut case (noun)
a whimsically eccentric person	a whimsically eccentric person