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.

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

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.

3. Not according to facts; inaccurate; erroneous.

Im*prop"er, v. t. To appropriate; to limit. [Obs.]

He would in like manner improper and inclose the sunbeams to comfort the rich and not the poor.

• To appropriate; to limit.
  
• 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.
  
• Not peculiar or appropriate to individuals; general; common.
  
• Not according to facts; inaccurate; erroneous.
  
• A non-planar group of four connected atoms in a molecule.