What is the meaning of smut?

noun

• A black colloidal substance consisting wholly or principally of amorphous carbon and used to make pigments and ink.
  • synonyms: carbon black, lampblack, soot, crock
• Destructive diseases of plants (especially cereal grasses) caused by fungi that produce black powdery masses of spores.
• Any fungus of the order Ustilaginales.
  • synonyms: smut fungus
• An offensive or indecent word or phrase.
  • synonyms: obscenity, vulgarism, filth, dirty word
• Creative activity (writing or pictures or films etc.) of no literary or artistic value other than to stimulate sexual desire.
  • synonyms: pornography, porno, porn, erotica

verb

• Make obscene.
  • usage: "This line in the play smuts the entire act"
• Stain with a dirty substance, such as soot.
• Become affected with smut.
  • usage: "the corn smutted and could not be eaten"
• Affect with smut or mildew, as of a crop such as corn. .