Where does “impropre” come from?

impropre (Middle French) comes from Latin improprius, from Latin in-, from Latin in, from Old Latin en, from Proto-Italic en, from Proto-Indo-European h₁én — in.

Ancestry of “impropre”, step by step

Step	Language	Word	Meaning
1	Latin	improprius	not proper; improper
2	Latin	in-	un-, non-, not; in, within, inside
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

Words derived from “impropre”

improper
improperly
improperness

Every word from Proto-Indo-European h₁én →Every word from Proto-Italic en →Every word from Latin in- →