Where does “Bitsilly” come from?

Bitsilly (Navajo) comes from Navajo atsilí, from Proto-Athabaskan *-kʸə̓tɬʼə.

Ancestry of “Bitsilly”, step by step

Step	Language	Word	Meaning
1	Navajo	atsilí	younger brother, little brother
2	Proto-Athabaskan	*-kʸə̓tɬʼə	—

Bitsilly — Etymology, Origin & Word History | Etymology Explorer