brainpan vs cranium

brainpan and cranium both are nouns.

Word	Noun	Adjective	Verb	Adverb
brainpan	Yes	No	No	No
cranium	Yes	No	No	No

As nouns, brainpan and cranium are synonyms defined as:

Other synonyms of brainpan include braincase.

brainpan (noun)	cranium (noun)
the part of the skull that encloses the brain	the part of the skull that encloses the brain