Where does “immersion” come from?

Immersion comes from Late Latin immersio, combining Latin in- (into) and mergere (to dip), ultimately from Proto-Indo-European h₁én (in).

immersion (English): The act of immersing or the condition of being...

Definitions

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