Latin word regulo comes from Proto-Indo-European *rek-, and later Proto-Indo-European *h₃réǵeti (To be straightening, to be setting upright.)

Detailed word origin of regulo

Dictionary entry	Language	Definition
*rek-	Proto-Indo-European (ine-pro)
*h₃réǵeti	Proto-Indo-European (ine-pro)	To be straightening, to be setting upright.
rego	Latin (lat)	I guide, steer. I oversee, manage. I rule, govern.
regula	Latin (lat)	Rule, bar.
regulo	Latin (lat)	To direct, regulate.