Source : Webster's Revised Unabridged Dictionary (1913)

Crust \Crust\ (kr?st), n. [L. crusta: cf. OF. crouste, F.
   cro[^u]te; prob. akin to Gr. ????? ice, E. crystal, from the
   same root as E. crude, raw. See {Raw}, and cf. {Custard}.]
   1. The hard external coat or covering of anything; the hard
      exterior surface or outer shell; an incrustation; as, a
      crust of snow.

            I have known the statute of an emperor quite hid
            under a crust of dross.               --Addison.

            Below this icy crust of conformity, the waters of
            infidelity lay dark and deep as ever. --Prescott.

   2. (Cookery)
      (a) The hard exterior or surface of bread, in distinction
          from the soft part or crumb; or a piece of bread grown
          dry or hard.
      (b) The cover or case of a pie, in distinction from the
          soft contents.
      (c) The dough, or mass of doughy paste, cooked with a
          potpie; -- also called {dumpling}.

                Th' impenetrable crust thy teeth defies.
                                                  --Dryden.

                He that keeps nor crust nor crumb. --Shak.

                They . . . made the crust for the venison pasty.
                                                  --Macaulay.

   3. (Geol.) The exterior portion of the earth, formerly
      universally supposed to inclose a molten interior.

   4. (Zo["o]l.) The shell of crabs, lobsters, etc.

   5. (Med.) A hard mass, made up of dried secretions blood, or
      pus, occurring upon the surface of the body.

   6. An incrustation on the interior of wine bottles, the
      result of the ripening of the wine; a deposit of tartar,
      etc. See {Beeswing}.

Crust \Crust\, v. t. [imp. & p. p. {Crusted}; p. pr. & vb. n.
   {Crusting}.] [Cf. OF. crouster, L. crustare. See {Crust}, n.
   ]
   To cover with a crust; to cover or line with an incrustation;
   to incrust.

         The whole body is crusted over with ice. --Boyle.

         And now their legs, and breast, and bodies stood
         Crusted with bark.                       --Addison.

         Very foul and crusted bottles.           --Swift.

         Their minds are crusted over, like diamonds in the
         rock.                                    --Felton.

Crust \Crust\, v. i.
   To gather or contract into a hard crust; to become incrusted.

         The place that was burnt . . . crusted and healed.
                                                  --Temple.

Source : WordNet®

crust
     n 1: the outer layer of the Earth [syn: {Earth's crust}]
     2: a hard outer layer that covers something [syn: {incrustation},
         {encrustation}]
     3: the trait of being rude and impertinent; inclined to take
        liberties [syn: {gall}, {impertinence}, {impudence}, {insolence},
         {cheekiness}, {freshness}]

crust
     v : form a crust or form into a crust; "The bread crusted in the
         oven"