pinhead vs dumbbell

pinhead and dumbbell both are nouns.

Word	Noun	Adjective	Verb	Adverb
pinhead	Yes	No	No	No
dumbbell	Yes	No	No	No

As nouns, pinhead and dumbbell are synonyms defined as:

Other synonyms of pinhead include boob, booby, dope, dummy.

pinhead (noun)	dumbbell (noun)
the head of a pin	an exercising weight; two spheres connected by a short bar that serves as a handle
an ignorant or foolish person	an ignorant or foolish person