An external coat or covering of a thing, which is hard or harder than the internal substance; as the crust of bread; the crust of snow; the crust of dross; the crust of a pie.

A piece of crust; a waste piece of bread.

A shell, as the hard covering of a crab and some other animals.

Ascab.

The superficial substances of the earth are, in geology, called its crust.

To cover with a hard case or coat; to spread over the surface a substance harder than the matter covered; to incrust; as, to crust a thing with clay; to crust cake with sugar; crusted with bark.

To cover with concretions.

To gather or contract into a hard covering; to concrete or freeze, as superficial matter.