Source : Webster's Revised Unabridged Dictionary (1913)

Scab \Scab\, v. i. [imp. & p. p. {Scabbed}; p. pr. & vb. n.
   {Scabbing}.]
   To become covered with a scab; as, the wound scabbed over.

Scab \Scab\ (sk[a^]b), n. [OE. scab, scabbe, shabbe; cf. AS.
   sc[ae]b, sceabb, scebb, Dan. & Sw. skab, and also L. scabies,
   fr. scabere to scratch, akin to E. shave. See {Shave}, and
   cf. {Shab}, {Shabby}.]
   1. An incrustation over a sore, wound, vesicle, or pustule,
      formed by the drying up of the discharge from the diseased
      part.

   2. The itch in man; also, the scurvy. [Colloq. or Obs.]

   3. The mange, esp. when it appears on sheep. --Chaucer.

   4. A disease of potatoes producing pits in their surface,
      caused by a minute fungus ({Tiburcinia Scabies}).

   5. (Founding) A slight irregular protuberance which defaces
      the surface of a casting, caused by the breaking away of a
      part of the mold.

   6. A mean, dirty, paltry fellow. [Low] --Shak.

   7. A nickname for a workman who engages for lower wages than
      are fixed by the trades unions; also, for one who takes
      the place of a workman on a strike. [Cant]

Scab \Scab\, n. (Bot.)
   Any one of various more or less destructive fungus diseases
   attacking cultivated plants, and usually forming dark-colored
   crustlike spots.

Source : WordNet®

scab
     n 1: someone who works (or provides workers) during a strike
          [syn: {strikebreaker}, {blackleg}, {rat}]
     2: the crustlike surface of a healing skin lesion

scab
     v 1: form a scab; "the wounds will eventually scab"
     2: take the place of work of someone on strike [syn: {rat}, {blackleg}]