Where does “прав ъгъл” come from?

прав ъгъл (Bulgarian) comes from Bulgarian пра́в, from Proto-Slavic pravъ, from Proto-Balto-Slavic prōˀwas, from Proto-Indo-European preh₃-wo-s, from Proto-Indo-European per-, from Proto-Indo-European pr̥tós — passed , crossed.

Ancestry of “прав ъгъл”, step by step

прав ъгъл traces back through two separate lines of ancestry.

via Bulgarian пра́в

StepLanguageWordMeaning
1Bulgarianпра́вstraight
2Proto-Slavicpravъright, straight; correct
3Proto-Balto-Slavicprōˀwas—
4Proto-Indo-Europeanpreh₃-wo-s—
5Proto-Indo-Europeanper-before, in front; first; to go through
6Proto-Indo-Europeanpr̥tóspassed , crossed

via Bulgarian ъгъл

StepLanguageWordMeaning
1Bulgarianъгълangle, corner
2Proto-Slavicǫgъlъcorner, angle
3Proto-Balto-Slavic*ángulas—
4Proto-Indo-Europeanh₂engulosjoint?
5Proto-Indo-Europeanh₂eng-curve, bend
Every word from Proto-Indo-European pr̥tós →Every word from Proto-Indo-European per- →Every word from Proto-Indo-European preh₃-wo-s →