noun.
The metal part that closes the breech end of the barrel of a breechloading gun and that is removed to insert a cartridge and replaced before firing.
The Century Dictionary and Cyclopedia
noun.
A movable piece at the breech of a breech-loading gun, which is withdrawn for the insertion of a cartridge and closed before firing, to receive the impact of the recoil. E. H.Knight. See cut under breech-loader.
the GNU version of the Collaborative International Dictionary of English
noun.
The movable piece which closes the breech of a breech-loading firearm, and resists the backward force of the discharge. It is withdrawn for the insertion of a cartridge, and closed again before the gun is fired.