To appropriate; to limit.
"The judge ruled that the law was improper because it appropriated powers from other branches and limited citizens' free speech rights."
not suitable or right or appropriate
"slightly improper to dine alone with a married man"
"improper medication"
"improper attire for the golf course"
not conforming to legality, moral law, or social convention
"an unconventional marriage"
"improper banking practices"
unsuitable to needs or circumstances; inappropriate; inapt
"The heavy winter coat was improper attire for a mild spring day."
In plain English: Improper means not following the right rules, manners, or laws for a specific situation.
"He was sent home for wearing improper clothing to church services."
Usage: Use improper when something is not suitable, correct, or ethical for the specific situation at hand. This adjective often describes behavior that violates social norms rather than simply being inconvenient.
The word improper comes from the Middle French impropre, which was borrowed directly from the Latin phrase meaning "not proper." Although it looks like a modern combination of the prefix in- and the adjective proper, its actual origin is an older form that has been in use since before English adopted these related words.