Source : Webster's Revised Unabridged Dictionary (1913)

Whisperer \Whis"per*er\, n.
   1. One who whispers.

   2. A tattler; one who tells secrets; a conveyer of
      intelligence secretly; hence; a backbiter; one who
      slanders secretly. --Prov. xvi. 28.

Source : WordNet®

whisperer
     n : one who speaks in a whisper