Latin crusta (“hard outer covering”) via Anglo-Norman and Old French cruste, from Proto-Indo-European *krus-to (“that which has been hardened”), from *kreus (“to form a crust, begin to freeze”), related to Old Norse hroðr (“scurf”), Old English hruse (“earth”), Old High German hrosa (“crust, ice”), Latvian kruwesis (“frozen mud”), Ancient Greek κρυο (“frost, icy cold”), κρύσταλλος (“crystal, ice”), Avestan xruzdra- (“hard”), Sanskrit क्रुड् (“thicken, make hard”)
crust (countable and uncountable; plural crusts)
- A more solid, dense or hard layer on a surface or boundary.
- The external layer of most types of bread.
- Outer layer composed of pastry
- Bread foundation of pizza
- (geology) The outermost layer of the lithosphere of the Earth.
- (uncountable) Nerve, gall.
- You've got a lot of crust standing there saying that.
- 1960, P. G. Wodehouse, Jeeves in the Offing, chapter XVIII:
- “Oh?” she said. “So you have decided to revise my guest list for me? You have the nerve, the – the –” I saw she needed helping out. “Audacity,” I said, throwing her the line. “The audacity to dictate to me who I shall have in my house.” It should have been “whom”, but I let it go. “You have the –” “Crust.” “– the immortal rind,” she amended, and I had to admit it was stronger, “to tell me whom” – she got it right that time – “I may entertain at Brinkley Court and who” – wrong again – “I may not.”
- crust punk (a subgenre of punk music)
any solid, hard surface layer
outer layer composed of pastry
bread foundation of pizza
outermost layer of a planet
Related terms 
crust (third-person singular simple present crusts, present participle crusting, simple past and past participle crusted)
- (transitive) To cover with a crust.
- (intransitive) To form a crust.