A more solid, dense or hard layer on a surface or boundary.

The external, hardened layer of certain foodstuffs, including most types of bread, fried meat, etc.

An outer layer composed of pastry

The bread-like base of a pizza.

(Britain, Australia, New Zealand, Ireland, Canada) A slice of bread cut from the end of a loaf; the heel.

(geology) The outermost layer of the lithosphere of the Earth.

(astronomy, by extension) The outermost layer of any terrestrial planet.

The shell of crabs, lobsters, etc.

(Britain, Australia, informal) A living.

(uncountable, informal) Nerve, gall.

(music) Ellipsis of crust punk (a subgenre of punk music)

(transitive) To cover with a crust.

(intransitive) To form a crust.