Where does “improper” come from?

Improper comes from Middle French impropre, from Latin improprius, composed of the Latin negative prefix in- and Latin proprius meaning "one's own," ultimately from Proto-Indo-European ne meaning "not."

improper (English): unsuitable to needs or circumstances;...

Definitions

unsuitable to needs or circumstances;...

Ancestry of “improper”, step by step

Step	Language	Word	Meaning
1	Middle French	impropre	—
2	Latin	improprius	not proper; improper
3	Latin	in-	un-, non-, not; in, within, inside
4	Latin	in	in, at, on, upon, from; within, while in; into,...
5	Old Latin	en	in
6	Proto-Italic	en	in
7	Proto-Indo-European	h₁én	in

Words derived from “improper”

improperly
improperness

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