Where does “improperly” come from?

Improperly derives from Middle French improprement, from Latin improprius meaning "not suitable," formed from the prefix in- and proprius meaning "one's own."

improperly (English): in an improper manner; not properly

Definitions

in an improper manner; not properly

Ancestry of “improperly”, step by step

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

Every word from Proto-Indo-European h₁én →

improperly — Etymology, Origin & Word History | Etymology Explorer