Etymology tree
Proto-Indo-European *ḱerh₂-
Proto-Indo-European *-ō
Proto-Indo-European *ḱr̥h₂-(e)s-n-
Proto-Hellenic *kárahə
Ancient Greek *κρᾱν- (*krān-)
Proto-Indo-European *-yósder.
Ancient Greek -ιος (-ios)?
Ancient Greek -ῐ́ον (-ĭ́on)
Ancient Greek κρᾱνῐ́ον (krānĭ́on)bor.
Medieval Latin crāniumlbor.
Portuguese crânio
Learned borrowing from Medieval Latin crānium, borrowed from Ancient Greek κρᾱνῐ́ον (krānĭ́on), from *κρᾱν- (*krān-) + -ῐ́ον (-ĭ́on).