suppressor
A firearm accessory designed to minimize audible report and muzzle flash. A suppressor basically consists of a tube that may screw or latch onto the end of a gun barrel and is filled with baffles that allow air otherwise pushed out the front of the gun to slow down and expand.
Suppressors are sometimes known as "silencers," but this is an exaggeration of the abilities of a suppressor to lessen sound. As long as bullet travels at supersonic speeds, it will still create the distinctive "boom." However, it is possible to make a very quiet weapon using subsonic ammunition, eliminating the sonic boom and thus the major source of loudness for a weapon.