crust

Short definition from Wiktionary

Noun

1. 1
   A more solid, dense or hard layer on a surface or boundary.
2. 2
   The external, hardened layer of certain foodstuffs, including most types of bread, fried meat, etc.
3. 3
   An outer layer composed of pastry
4. 4
   The bread-like base of a pizza.
5. 5
   A slice of bread cut from the end of a loaf; the heel.
6. 6
   The outermost layer of the lithosphere of the Earth.
7. 7
   The outermost layer of any terrestrial planet.
8. 8
   The shell of crabs, lobsters, etc.
9. 9
   A living.
10. 10
    Nerve, gall.
11. 11
    The head.
12. 12
    Ellipsis of crust punk, a subgenre of punk music.

Verb

1. 1
   To cover with a crust.
2. 2
   To form a crust.