1. Foul matter, like soot or coal dust; also, a spot or soil made by such matter.
2. (Science: chemical) bad, soft coal, containing much earthy matter, found in the immediate locality of faults.
3. (Science: botany) 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.
Origin: 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, and cf. Smitt, Smutch.