Source : Webster's Revised Unabridged Dictionary (1913)

Informant \In*form"ant\, n. [L. informans, -antis, p. pr. of
   informare. See {Inform}, v. t.]
   1. One who, or that which, informs, animates, or vivifies.
      [Obs.] --Glanvill.

   2. One who imparts information or instruction.

   3. One who offers an accusation; an informer. See {Informer}.
      [Obs. or R.]

            It was the last evidence of the kind; the informant
            was hanged.                           --Burke.

Source : WordNet®

informant
     n 1: a person who supplies information [syn: {source}]
     2: someone who sees an event and reports what happened [syn: {witness},
         {witnesser}]