Source : Webster's Revised Unabridged Dictionary (1913)

Hush \Hush\, n.
   Stillness; silence; quiet. [R.] ``It is the hush of night.''
   --Byron.

   {Hush money}, money paid to secure silence, or to prevent the
      disclosure of facts. --Swift.

Source : WordNet®

hush money
     n : a bribe paid to someone to insure that something is kept
         secret