crust

(noun) the outer layer of the Earth. Synonyms: Earth's crust.

(noun) a hard outer layer that covers something. Synonyms: incrustation, encrustation.

(noun) the trait of being rude and impertinent; inclined to take liberties. Synonyms: gall, impertinence, impudence, insolence, cheekiness, freshness.

(verb) form a crust or form into a crust. Examples: "The bread crusted in the oven."