Synonyms for Crust (same or very similar meaning)
WordNet sense 1 (a hard outer layer that covers something):
encrustation, incrustationWordNet sense 2 (the outer layer of the Earth):
Earth's crustWordNet sense 3 (the trait of being rude and impertinent; inclined to take liberties):
cheekiness, freshness, gall, impertinence, impudence, insolenceFrom the ODE community, based on WordNetadd/edit