Source : Webster's Revised Unabridged Dictionary (1913)

Impure \Im*pure"\, a. [L. impurus; pref. im- not + purus pure:
   cf. F. impur. See {Pure}.]
   1. Not pure; not clean; dirty; foul; filthy; containing
      something which is unclean or unwholesome; mixed or
      impregnated extraneous substances; adulterated; as, impure
      water or air; impure drugs, food, etc.

   2. Defiled by sin or guilt; unholy; unhallowed; -- said of
      persons or things.

   3. Unchaste; lewd; unclean; obscene; as, impure language or
      ideas. ``Impure desires.'' --Cowper.

   4. (Script.) Not purified according to the ceremonial law of
      Moses; unclean.

   5. (Language) Not accurate; not idiomatic; as, impure Latin;
      an impure style.

Impure \Im*pure"\, v. t.
   To defile; to pollute. [Obs.] --Bp. Hall.

Source : WordNet®

impure
     adj 1: combined with extraneous elements [ant: {pure}]
     2: used of persons or behaviors; not morally pure; "impure
        thoughts" [ant: {pure}]
     3: ritually unclean or impure; "and the swine...is unclean to
        you"-Leviticus 11:3 [syn: {unclean}] [ant: {clean}]