Source : Webster's Revised Unabridged Dictionary (1913)

Improper \Im*prop"er\, a. [F. impropre, L. improprius; pref. im-
   not + proprius proper. See {Proper}.]
   1. Not proper; not suitable; not fitted to the circumstances,
      design, or end; unfit; not becoming; incongruous;
      inappropriate; indecent; as, an improper medicine;
      improper thought, behavior, language, dress.

            Follow'd his enemy king, and did him service,
            Improper for a slave.                 --Shak.

            And to their proper operation still, Ascribe all
            Good; to their improper, Ill.         --Pope.

   2. Not peculiar or appropriate to individuals; general;
      common. [Obs.]

            Not to be adorned with any art but such improper
            ones as nature is said to bestow, as singing and
            poetry.                               --J. Fletcher.

   3. Not according to facts; inaccurate; erroneous.

   {Improper diphthong}. See under {Diphthong}.

   {Improper feud}, an original feud, not earned by military
      service. --Mozley & W.

   {Improper fraction}. See under {Fraction}.