shell

• shell [countable]
• 1
• a) the hard outer part that covers and protects an egg, nut, or seed:
• Never buy eggs with cracked shells.
• peanuts roasted in their shells
• b) the hard protective covering of an animal such as a snail, mussel, orcrab:
• a snail shell
• The children were collecting shells on the beach.
• ➔ seashell
• 2 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 English a metal tube containing a bullet and an explosive substance [= cartridge]
• 4 the outside structure of something, especially the part of a building that remains when the rest of it has been destroyed
• shell of
• the burnt-out shell of a nightclub
• 5

   out of your shell

  becoming less shy and more confident and willing to talk to people:
• I had hoped that university would bring him out of his shell.
• She's started to come out of her shell a little.

Definition from the Longman Dictionary of Contemporary English