Cap (noun)

1. A covering for the head, typically made of cloth.
2. A protective cover or seal for the end of a tube or pipe.
3. A top or upper limit, beyond which something cannot or should not exceed.

Origin:

Old english cæppe, of germanic origin; related to dutch kap and german kappe.

Examples:

1. He was wearing a baseball cap.
2. I need a new cap for my pen.
3. The government has set a cap on the number of refugees that can be accepted.
4. The cap of a mushroom is the upper part that covers the stem.
5. The cap of a bottle is used to seal the contents.