Pronunciation: (im-prop'ur),[key] —adj. 1. not proper; not strictly belonging, applicable, correct, etc.; erroneous: He drew improper conclusions from the scant evidence. 2. not in accordance with propriety of behavior, manners, etc.: improper conduct at a funeral. 3. unsuitable or inappropriate, as for the purpose or occasion: improper attire for a formal dance. 4. abnormal or irregular: improper functioning of the speech mechanism.