1. to behave in a way that is not appropriate, correct, or acceptable according to social or professional standards
The official was accused of acting improperly with company funds.
O funcionário foi acusado de agir indevidamente com os fundos da empresa.
2. to conduct oneself in a manner that violates rules, ethics, or decorum
She acted improperly during the formal dinner.
Ela agiu indevidamente durante o jantar formal.