unthinking vs stupid

unthinking is not a noun while stupid is a noun.

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

unthinking (noun)	stupid (noun)
	a person who is not very bright

unthinking (adjective)	stupid (adjective)
without care or thought for others	lacking or marked by lack of intellectual acuity
mentally sluggish	lacking intelligence
not exhibiting or characterized by careful thought	in a state of mental numbness especially as resulting from shock

unthinking (adverb)	stupid (adverb)
in a thoughtless manner