Where does “em” come from?

em (Portuguese) comes from Old Portuguese en, from Latin în, from Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

em (Portuguese): in; inside; within; on; on top of; in; at

Definitions

Step	Language	Word	Meaning
1	Old Portuguese	en	in
2	Latin	în	in, at, on, upon, from (space)
3	Latin	en	lookǃ beholdǃ; reallyǃ?; come onǃ
4	Proto-Italic	en	in
5	Proto-Indo-European	h₁én	in