Suppressor

A suppressor, or better known as the silencer, is a device attached to a firearm's barrel to reduce the amount of noise, flash, and recoil generated by the firing of the weapon.

It takes the form of a cylindrical metal tube that fits onto the firearm's barrel, with various internal mechanisms to significantly decrease muzzle flash and recoil, giving the weapon a barely noticeable sound, and increasing stealth applications.

Appearances in Halo
The Suppressor does not appear anywhere in the series, although it is mentioned in The Art of Halo, on the M7S Submachine Gun, a variant of the M7.

Trivia

 * The original plan for the suppressor, which was during World War II, was to modify the sound of the weapon firing into a different, unrecognizable sound, rather than to "silence" the weapon.
 * It is unknown if the suppressor is attached to any other UNSC weapons, such as the SRS sniper series, or if the Covenant have a counterpart of this particular attachment.