The Collaborative International Dictionary of English v.0.48:

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.
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            I have known the statute of an emperor quite hid
            under a crust of dross.               --Addison.
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            Below this icy crust of conformity, the waters of
            infidelity lay dark and deep as ever. --Prescott.
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   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.
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                Th' impenetrable crust thy teeth defies.
                                                  --Dryden.
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                He that keeps nor crust nor crumb. --Shak.
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                They . . . made the crust for the venison pasty.
                                                  --Macaulay.
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   3. (Geol.) The exterior portion of the earth, formerly
      universally supposed to inclose a molten interior.
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   4. (Zool.) The shell of crabs, lobsters, etc.
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   5. (Med.) A hard mass, made up of dried secretions blood, or
      pus, occurring upon the surface of the body.
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   6. An incrustation on the interior of wine bottles, the
      result of the ripening of the wine; a deposit of tartar,
      etc. See Beeswing.
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The Collaborative International Dictionary of English v.0.48:

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.
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         The whole body is crusted over with ice. --Boyle.
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         And now their legs, and breast, and bodies stood
         Crusted with bark.                       --Addison.
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         Very foul and crusted bottles.           --Swift.
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         Their minds are crusted over, like diamonds in the
         rock.                                    --Felton.
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The Collaborative International Dictionary of English v.0.48:

Crust \Crust\, v. i.
   To gather or contract into a hard crust; to become incrusted.
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         The place that was burnt . . . crusted and healed.
                                                  --Temple.
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WordNet (r) 3.0 (2006):

crust
    n 1: the outer layer of the Earth [syn: crust, Earth's
         crust]
    2: a hard outer layer that covers something [syn: crust,
       incrustation, encrustation]
    3: the trait of being rude and impertinent; inclined to take
       liberties [syn: crust, gall, impertinence, impudence,
       insolence, cheekiness, freshness]
    v 1: form a crust or form into a crust; "The bread crusted in
         the oven"