stupid vs simpleton

stupid and simpleton both are nouns.

Word	Noun	Adjective	Verb	Adverb
stupid	Yes	Yes	No	No
simpleton	Yes	No	No	No

As nouns, simpleton is a hypernym of stupid; that is, simpleton is a word with a broader meaning than stupid:

Other hypernyms of stupid include simple.

stupid (noun)	simpleton (noun)
a person who is not very bright	a person lacking intelligence or common sense

stupid (adjective)	simpleton (adjective)
lacking or marked by lack of intellectual acuity
lacking intelligence
in a state of mental numbness especially as resulting from shock