Where does “immersio” come from?

immersio (Late Latin) comes from Latin immergo, from Latin in, from Old Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

immersio (Late Latin): dipping; immersion

Definitions

Step	Language	Word	Meaning
1	Latin	immergo	I immerse; I plunge into
2	Latin	in	in, at, on, upon, from; within, while in; into,...
3	Old Latin	en	in
4	Proto-Italic	en	in
5	Proto-Indo-European	h₁én	in