impractical vs screwball

impractical is not a noun while screwball is a noun.

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

impractical (noun)	screwball (noun)
	a pitch with reverse spin that curves toward the side of the plate from which it was thrown
	a whimsically eccentric person

impractical (adjective)	screwball (adjective)
not practical; not workable or not given to practical matters	foolish; totally unsound
not practical or realizable; speculative