noun

• (archaic) Dirt, or a stain.
  "Too often, in the years between 800 and 1050, the everyday sun declined through the smirch of flame and smoke of a monastery or town robbed and burnt."
• (figurative, archaic) A stain on somebody's reputation.
  "there were some business transactions which savored of dangerous speculation, if not dishonesty; and around it all lay the smirch of the Freedmen's Bank."

verb

• (transitive, archaic) To dirty; to make dirty.
  "CELIA. I'll put myself in poor and mean attire, / And with a kind of umber smirch my face; / The like do you; so shall we pass along, / And never stir assailants."
• (transitive, figurative, archaic) To harm the reputation of; to smear or slander.

noun

• (astronomy) 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)
  "The strain h(t) produced by a smirch in LISA is given by h(t) = −-A(t)cos[(t) + φ(t)]"