Where does “नियमित” come from?

नियमित (Sanskrit) comes from Sanskrit नियम, from Sanskrit नि-, from Proto-Indo-Iranian ní, from Proto-Indo-European ni — down.

Ancestry of “नियमित”, step by step

Step	Language	Word	Meaning
1	Sanskrit	नियम	restraining, checking, holding back, preventing,...
2	Sanskrit	नि-	into; down; without, free of
3	Proto-Indo-Iranian	ní	down, downwards; in, into
4	Proto-Indo-European	ni	down

नियमित — Etymology, Origin & Word History | Etymology Explorer