stupid vs blockhead

stupid and blockhead both are nouns.

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

As nouns, blockhead is a hyponym of stupid; that is, blockhead is a word with a more specific, narrower meaning than stupid:

stupid: a person who is not very bright
blockhead: a stupid person; these words are used to express a low opinion of someone's intelligence

stupid (noun)	blockhead (noun)
a person who is not very bright	a stupid person; these words are used to express a low opinion of someone's intelligence

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