Where does “शीला” come from?

शीला (Hindi) comes from Sanskrit शील, from Sanskrit शी, from Proto-Indo-European ḱey- — to be lying down; to settle.

Ancestry of “शीला”, step by step

Step	Language	Word	Meaning
1	Sanskrit	शील	conduct, disposition, nature, tendency; custom,...
2	Sanskrit	शी	to lie down
3	Proto-Indo-European	ḱey-	to be lying down; to settle

शीला — Etymology, Origin & Word History | Etymology Explorer