Where does “César” come from?

César (Spanish) comes from Latin Caesar, from Latin caesaries, from Proto-Indo-European kéysero- — hair.

Ancestry of “César”, step by step

Step	Language	Word	Meaning
1	Latin	Caesar	Julius Caesar; emperor
2	Latin	caesaries	or hair
3	Proto-Indo-European	kéysero-	hair

César — Etymology, Origin & Word History | Etymology Explorer