Cap

A usually soft and close-fitting head covering, either having no brim or with a visor. I seldom wear a cap.
2. A protective cover or seal, especially one that closes off an end or a tip. You need a tool to remove a bottle cap.
3. A summit or top, as of a mountain. Snow covered the cap of the mountain.
4. Botany. The top part of a mushroom. The cap of some mushrooms are edible.
5. A small explosive charge enclosed in paper for use in a toy gun. As a child we had a cap gun.