(1):

(n.) Any of various devices to silence the humming noise of telegraph wires.

(2):

(n.) The muffler of an internal-combustion engine.

(3):

(n.) One that silences;

(4):

(n.) 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.