Webster's Revised Unabridged Dictionary · 1913

Improper

Improper , adjective

[French impropre, Latin 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. — Shakespeare
And to their proper operation still, Ascribe all Good; to their improper, Ill. — Pope
2.
Not peculiar or appropriate to individuals; general; common. [Obsolete]
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.
Collocations (3)
Improper diphthong , See under Diphthong.
Improper feud , an original feud, not earned by military service. — Mozley & W
Improper fraction , See under Fraction.

Improper , transitive verb

To appropriate; to limit. [Obsolete]
He would in like manner improper and inclose the sunbeams to comfort the rich and not the poor. — Jewel