Dirt, or a stain. / (figuratively) A stain on somebody's reputation.

(transitive) To dirty; to make dirty. / (transitive, figuratively) To harm the reputation of; to smear or slander.

A chirp of radiation power from an astronomical body that has a smeared appearance on its plot in the time-frequency plane (usually associated with massive bodies orbiting supermassive black holes)

present participle of smirch

Third-person singular simple present indicative form of smirch

simple past tense and past participle of smirch

Without a smirch; unsmirched.