SMUT

noun

1. Soot.
2. A flake of ash or soot.
3. Sexually vulgar material; something that is sexual in a dirty way; pornographic material.

verb

1. To stain (or be stained) with soot or other dirt.
2. To taint (grain, etc.) with the smut fungus.
3. To become tainted by the smut fungus.