Where does “Мо́кошь” come from?

Мо́кошь (Russian) comes from Old East Slavic Мокошь, from Proto-Slavic *Mokošь.

Ancestry of “Мо́кошь”, step by step

Step	Language	Word	Meaning
1	Old East Slavic	Мокошь	—
2	Proto-Slavic	*Mokošь	—