1 a : the hard outer covering of an animal, insect, etc., that protects it [count] ▪ a turtle's shell ▪ the shell of a crab ▪ We collected shells at the beach. [noncount] ▪ jewelry made of shell — see also seashell, tortoiseshell
b : the hard outer covering of an egg : eggshell [count] ▪ broken shells [noncount] ▪ a piece of shell
c : the hard outer covering of a nut, fruit, or seed [count] ▪ a coconut shell [noncount] ▪ pieces of walnut shell 2 [count] US : something (such as pasta) that is shaped like a shell
▪ We're going to have stuffed shells for dinner. 3 [count] : the hard outer structure of a building, car, airplane, etc. — usually singular ▪ the shell of an unfinished house ▪ the shell of an airplane ▪ The building was just a bombed-out shell. 4 [count] chiefly US : a hard or crisp piece of bread, dough, etc., that is used to hold a filling
▪ a pastry/pie shell ▪ taco/tortilla shells 5 [count] a : a metal case that is filled with an explosive and that is shot from a cannon
▪ mortar shells
b chiefly US : a metal tube that you put into a gun and that holds an explosive and a bullet : cartridge
▪ The police found several spent shells at the scene of the shooting. 6 a — used in phrases that describe becoming less shy and more willing to talk to other people ▪ Making new friends helped her come out of her shell. = Making new friends brought her out of her shell.
b — used in phrases that describe becoming quieter, less active, etc. ▪ He lost confidence in himself and retreated/withdrew into his shell.