Where does “по́чка” come from?

по́чка (Russian) comes from Old Russian почька, from Proto-Slavic pъťьka.

Ancestry of “по́чка”, step by step

Step	Language	Word	Meaning
1	Old Russian	почька	—
2	Proto-Slavic	pъťьka	—

по́чка — Etymology, Origin & Word History | Etymology Explorer