bump stock

[ buhmp stok ]
/ ˈbʌmp ˌstɒk /

noun

a replacement gunstock that enables a semiautomatic rifle to discharge bullets at a much higher rate of fire, nearly that of a fully automatic machine gun.

Origin of bump stock

First recorded in 2005–10; short for bump fire (from its use of the recoil to bump the trigger against the trigger finger) + (gun)stock
Also called bump-fire stock [buhmp-fahyer stok] /ˈbʌmpˌfaɪər ˌstɒk/.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019