​SHELL (O. Eng. scell, scyll, cf. Du. schel, shell, Goth. skalja, tile; the word means originally a thin flake, cf. Swed. skalja, to peel off; it is allied to "scale" and "skill," from a root meaning to cleave, divide, separate), the hard outside natural covering of anything, as of some fruits and seeds; more particularly, the conch (q.v.) or integument which acts as a defence for the bodies of various animals (see Mollusca, Gastropoda, Malacostraca, &c.), the test, crust or carapace; also the outer covering of an egg. The word is also used of many objects resembling the natural shell in use or shape, and especially of a hollow projectile filled with explosives (see Ammunition, § Shell, and Ordnance).