Missile that may be found on the beach (5)
I believe the answer is:
shell
'missile' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for shell that I've seen before include "Bit of explosive" , "Mortar missile" , "Hard protective case" , "Tortoise's home" , "attack with bombs" .)