thick-skulled vs stupid

thick-skulled is not a noun while stupid is a noun.

Word	Noun	Adjective	Verb	Adverb
thick-skulled	No	Yes	No	No
stupid	Yes	Yes	No	No

thick-skulled (noun)	stupid (noun)
	a person who is not very bright

thick-skulled (adjective)	stupid (adjective)
(used informally) stupid	lacking or marked by lack of intellectual acuity
	lacking intelligence
	in a state of mental numbness especially as resulting from shock