Source : Webster's Revised Unabridged Dictionary (1913)

Smut \Smut\, v. t. [imp. & p. p. {Smutted}; p. pr. & vb. n.
   {Smutting}.]
   1. To stain or mark with smut; to blacken with coal, soot, or
      other dirty substance.

   2. To taint with mildew, as grain. --Bacon.

   3. To blacken; to sully or taint; to tarnish.

   4. To clear of smut; as, to smut grain for the mill.

Smut \Smut\, v. i.
   1. To gather smut; to be converted into smut; to become
      smutted. --Mortimer.

   2. To give off smut; to crock.

Smut \Smut\, n. [Akin to Sw. smuts, Dan. smuds, MHG. smuz, G.
   schmutz, D. smet a spot or stain, smoddig, smodsig,
   smodderig, dirty, smodderen to smut; and probably to E.
   smite. See {Smite}, v. t., and cf. {Smitt}, {Smutch}.]
   1. Foul matter, like soot or coal dust; also, a spot or soil
      made by such matter.

   2. (Mining) Bad, soft coal, containing much earthy matter,
      found in the immediate locality of faults.

   3. (Bot.) An affection of cereal grains producing a swelling
      which is at length resolved into a powdery sooty mass. It
      is caused by parasitic fungi of the genus {Ustilago}.
      {Ustilago segetum}, or {U. Carbo}, is the commonest kind;
      that of Indian corn is {Ustilago maydis}.

   4. Obscene language; ribaldry; obscenity.

            He does not stand upon decency . . . but will talk
            smut, though a priest and his mother be in the room.
                                                  --Addison.

   {Smut mill}, a machine for cleansing grain from smut.

Source : WordNet®

smut
     n 1: a black colloidal substance consisting wholly or principally
          of amorphous carbon and used to make pigments and ink
          [syn: {carbon black}, {lampblack}, {soot}]
     2: destructive diseases of plants (especially cereal grasses)
        caused by fungi that produce black powdery masses of
        spores
     3: any fungus of the order Ustilaginales [syn: {smut fungus}]
     4: creative activity (writing or pictures or films etc.) of no
        literary or artistic value other than to stimulate sexual
        desire [syn: {pornography}, {porno}, {porn}, {erotica}]
     [also: {smutting}, {smutted}]

smut
     v 1: make obscene; "This line in the play smuts the entire act"
     2: stain with a dirty substance, such as soot
     3: become affected with smut; "the corn smutted and could not
        be eaten"
     4: affect with smut or mildew, as of a crop such as corn
     [also: {smutting}, {smutted}]