shell
Definitions
A hard, protective outer layer created by an animal, such as a mollusk, crustacean, or egg.
A rigid outer covering or framework of an object, building, or vehicle.
A metal case filled with explosive or other substances, designed to be fired from a large gun.
Examples
The children spent the afternoon collecting seashells along the sandy shore.
You need to crack the shell of the walnut to get to the nut inside.
The turtle retreated into its hard shell whenever it felt threatened.