Where does “ศีลอด” come from?

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

ศีลอด (Thai): sawm

Definitions

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

ศีลอด — Etymology, Origin & Word History | Etymology Explorer