In The Bells of St. Mary's there isn't a hint of impropriety.
Hoover preached that even the appearance of impropriety must be avoided.
So far Mitt Romney has run a careful, disciplined campaign that has avoided the slightest whiff of impropriety.
1610s, "quality or fact of being improper," from French impropriété (16c.), from Latin improprietas, from improprius (see improper). As "improper thing," 1670s.