The only free and comprehensive online etymological dictionary of the Spanish language
cerebro m. (Noun) "brain," "cerebrum"
13th cent. From Latin cerebrum "brain." From Proto-Italic *kerasro- 'id.' From Proto-Indo-European *ḱerh2-s-ro- "brain," but more literally "the thing in the head." From *ḱerh2-s- "head." From an ancient root *ḱer- "head," from which *ḱer-n- "horn" is also derived (see cuerno).
Indo-European
Germanic
Old Norse hjarni "brain," Old English hærn (English harns)
Hellenic
Ancient Greek κέρας (kéras) "drinking horn," "horn trumpet" (from *ḱer-h2-s-)
Armenian
Armenian sar
Indo-Iranian
Sanskrit śíras-, Young Avestan sarah-

As a modern extended metaphor for a person, cerebro can mean "nerd," "brainiac."