smut

noun

1. a particle of soot; sooty matter.
2. a black or dirty mark; smudge.
3. indecent language or publications; obscenity.
4. Plant Pathology.
   1. a disease of plants, especially cereal grasses, characterized by the conversion of affected parts into black, powdery masses of spores, caused by fungi of the order Ustilaginales.
   2. a fungus causing this disease.