The Collaborative International Dictionary of English v.0.48:

Scab \Scab\ (sk[a^]b), n. [OE. scab, scabbe, shabbe; cf. AS.
   scaeb, 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.
      [1913 Webster]

   2. The itch in man; also, the scurvy. [Colloq. or Obs.]
      [1913 Webster]

   3. The mange, esp. when it appears on sheep. --Chaucer.
      [1913 Webster]

   4. A disease of potatoes producing pits in their surface,
      caused by a minute fungus (Tiburcinia Scabies).
      [1913 Webster]

   5. (Founding) A slight irregular protuberance which defaces
      the surface of a casting, caused by the breaking away of a
      part of the mold.
      [1913 Webster]

   6. A mean, dirty, paltry fellow. [Low] --Shak.
      [1913 Webster]

   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]
      [1913 Webster]

   8. (Bot.) Any one of various more or less destructive fungus
      diseases attacking cultivated plants, and usually forming
      dark-colored crustlike spots.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Scab \Scab\, v. i. [imp. & p. p. Scabbed; p. pr. & vb. n.
   Scabbing.]
   1. To become covered with a scab; as, the wound scabbed over.
      [1913 Webster]

   2. to take the place of a striking worker.
      [PJC]

WordNet (r) 3.0 (2006):

scab
    n 1: someone who works (or provides workers) during a strike
         [syn: scab, strikebreaker, blackleg, rat]
    2: the crustlike surface of a healing skin lesion
    v 1: form a scab; "the wounds will eventually scab"
    2: take the place of work of someone on strike [syn: fink,
       scab, rat, blackleg]

Moby Thesaurus II by Grady Ward, 1.0:

134 Moby Thesaurus words for "scab":
   abscess, aposteme, bed sore, birthmark, blackhead, blackleg, blain,
   bleb, blemish, blister, boil, bubo, bulla, bunion, canker,
   canker sore, carbuncle, chancre, chancroid, check, chilblain,
   cicatrix, cicatrize, close up, cold sore, comedo, crack, crater,
   craze, crust, deface, defacement, defect, deform, deformation,
   deformity, disfiguration, disfigure, disfigurement, distort,
   distortion, effloresce, encrust, eschar, fault, felon, fester,
   festering, fever blister, fink, fistula, flaw, freckle, furuncle,
   furunculus, gathering, granulate, gumboil, heal, heal over,
   hemangioma, hemorrhoids, hickey, incrust, incrustation, keloid,
   kibe, kink, knit, lentigo, lesion, loricate, mar, milium, mole,
   needle scar, nevus, papula, papule, paronychia, parulis,
   pastry shell, petechia, piecrust, piles, pimple, pit, pock,
   pockmark, polyp, port-wine mark, port-wine stain, pustule, rat,
   rift, right itself, rising, scab over, scale, scar, scarify,
   scratch, sebaceous cyst, set, shell, soft chancre, sore, split,
   stalactite, stalagmite, stigma, strawberry mark, strikebreaker,
   sty, suppuration, swelling, track, tubercle, twist, ulcer,
   ulceration, verruca, vesicle, wale, warp, wart, weal, welt, wen,
   wheal, whelk, whitehead, whitlow, wound