Source : Webster's Revised Unabridged Dictionary (1913)

Silencer \Si"lenc*er\, n.
   One that silences; specif.:
   (a) The muffler of an internal-combustion engine.
   (b) Any of various devices to silence the humming noise of
       telegraph wires.
   (c) A device for silencing the report of a firearm shooting
       its projectiles singly, as a tubular attachment for the
       muzzle having circular plates that permit the passage of
       the projectile but impart a rotary motion to, and thus
       retard, the exploding gases.

Source : WordNet®

silencer
     n 1: short tube attached to the muzzle of a gun that deadens the
          sound of firing
     2: a tubular acoustic device inserted in the exhaust system
        that is designed to reduce noise [syn: {muffler}]