Source : Webster's Revised Unabridged Dictionary (1913)

Impropriety \Im`pro*pri"e*ty\, n.; pl. {Improprieties}. [L.
   improprietas; cf. F. impropri['e]t['e]. See {Improper}.]
   1. The quality of being improper; unfitness or unsuitableness
      to character, time place, or circumstances; as,
      impropriety of behavior or manners.

   2. That which is improper; an unsuitable or improper act, or
      an inaccurate use of language.

            But every language has likewise its improprieties
            and absurdities.                      --Johnson.

            Many gross improprieties, however authorized by
            practice, ought to be discarded.      --Swift.

Source : WordNet®

impropriety
     n 1: an improper demeanor [syn: {improperness}] [ant: {propriety},
           {propriety}]
     2: an indecent or improper act [syn: {indecency}]
     3: an act of undue intimacy [syn: {familiarity}, {indecorum}, {liberty}]