The term 'STOCK OF GUN' can be broken down into two crossword solutions: BUTT (4 letters). The term 'BUTT' in this context refers to the back part of a gun, which is typically made of wood or plastic and is used to support the gun when it is fired. It also helps to absorb some of the recoil from the gun when it is fired. The stock of a gun is an important part of the gun, as it helps to provide stability and accuracy when shooting.