noun

• (colloquial or obsolete) The scabies.
• (uncountable) Any of several different diseases of potatoes producing pits and other damage on their surface, caused by streptomyces bacteria (but formerly believed to be caused by a fungus).
• (phytopathology) Any one of various more or less destructive fungal diseases that attack cultivated plants, forming dark-colored crustlike spots.
• (founding) A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.

verb

• (intransitive) To become covered by a scab or scabs.
• (intransitive) To form into scabs and be shed, as damaged or diseased skin.
  "1734, Royal Society of London, The Philosophical Transactions (1719 - 1733) Abridged, Volume 7, page 631, Thoſe Puſtules aroſe, maturated, and ſcabbed off, intirely like the true Pox."
• (transitive) To remove part of a surface (from).
  "The beds shall be scabbed off to give a solid bearing, no pinning shall be admitted between the backing and the face stones and there shall be a good square joint not exceeding one inch in width, and the face stone shall be scabbed off to allow this."
• (intransitive) To act as a strikebreaker.
  "Don't scab for the bosses / Don't listen to their lies / Us poor folks haven't got a chance / Unless we organize."