Where does “потайной” come from?

потайной (Russian) comes from Russian потаи́ть, from Russian по́-, from Russian -бира́ть.

потайной (Russian): hidden, secret

Definitions

Step	Language	Word	Meaning
1	Russian	потаи́ть	—
2	Russian	по́-	—
3	Russian	-бира́ть	—

потайной — Etymology, Origin & Word History | Etymology Explorer