Where does “pro” come from?

pro (Old Czech) comes from Proto-Slavic *pro, from Proto-Balto-Slavic *pra, from Proto-Indo-European pró, from Proto-Indo-European per-, from Proto-Indo-European pr̥tós — passed , crossed.

Ancestry of “pro”, step by step

StepLanguageWordMeaning
1Proto-Slavic*profor
2Proto-Balto-Slavic*pra—
3Proto-Indo-Europeanprótoward, leading to
4Proto-Indo-Europeanper-before, in front; first; to go through
5Proto-Indo-Europeanpr̥tóspassed , crossed

Words derived from “pro”

Every word from Proto-Indo-European pr̥tós →Every word from Proto-Indo-European per- →Every word from Proto-Indo-European pró →