Where does “sag” come from?

sag (Middle Persian) comes from Old Persian ??, from Proto-Iranian cwā́, from Proto-Indo-Iranian ćwā́, from Proto-Indo-European ḱwṓ — dog.

Ancestry of “sag”, step by step

StepLanguageWordMeaning
1Old Persian??—
2Proto-Iraniancwā́dog
3Proto-Indo-Iranianćwā́dog
4Proto-Indo-Europeanḱwṓdog
Every word from Proto-Indo-European ḱwṓ →Every word from Proto-Indo-Iranian ćwā́ →Every word from Proto-Iranian cwā́ →