scab

Short definition from Wiktionary

Noun

1. 1
   An incrustation over a sore, wound, vesicle, or pustule, formed during healing.
2. 2
   The scabies.
3. 3
   The mange, especially when it appears on sheep.
4. 4
   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).
5. 5
   Common scab, a relatively harmless variety of scab (potato disease) caused by Streptomyces scabies.
6. 6
   Any one of various more or less destructive fungal diseases that attack cultivated plants, forming dark-colored crustlike spots.
7. 7
   A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.
8. 8
   A mean, dirty, paltry fellow.
9. 9
   A worker who acts against trade union policies; any picket crosser (strikebreaker), and especially one with devotion to union busting.

Verb

1. 1
   To become covered by a scab or scabs.
2. 2
   To form into scabs and be shed, as damaged or diseased skin.
3. 3
   To remove part of a surface (from).
4. 4
   To act as a strikebreaker.
5. 5
   To beg (for), to cadge or bum.