Where does “Baikal” come from?

Baikal comes from Russian Байка́л, borrowed from Buryat Байгал, which derives from Proto-Turkic bāj.

Ancestry of “Baikal”, step by step

Step	Language	Word	Meaning
1	Russian	Байка́л	Baikal
2	Buryat	Байгал	—

Baikal — Etymology, Origin & Word History | Etymology Explorer