Hammer

1. A hand tool with a heavy rigid head and a handle; used to deliver an impulsive force by striking. The hammer should be taken care of; do not let it rust.
2. The part of a gunlock that hits the primer of firing pin or explodes the percussion cap and causes the gun to fire. The hammer is vital to the weapon and your safety.
3. One of the padded wooden pieces of a piano that strikes the strings. A piano needs 88 hammers in good condition to keep the piano in tune.