the hard outer part that covers and protects an egg, nut, or seed:
Never buy eggs with cracked shells.
peanuts roasted in their shells
the hard protective covering of an animal such as a snail, mussel, or crab:
a snail shell
The children were collecting shells on the beach.
a metal container, like a large bullet, which is full of an explosive substance and is fired from a large gun:
We ran for cover as shells dropped all around us.
an exploding mortar shell
3 especially American EnglishPMW
a metal tube containing a bullet and an explosive substance [= cartridge]
the outside structure of something, especially the part of a building that remains when the rest of it has been destroyed
the burnt-out shell of a nightclub