A Scab

1. An incrustation over a sore, wound, vesicle, or pustule, formed during healing.
2. (colloquial or obsolete) The scabies.
3. The mange, especially when it appears on sheep.
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. Common scab, a relatively harmless variety of scab (potato disease) caused by *Streptomyces scabies*.
6. (phytopathology) Any one of various more or less destructive fungal diseasesthat attack cultivated plants, forming dark-colored crustlike spots.
7. (founding) A slight irregular protuberancewhich defaces the surface of a casting, caused by the breaking away of a part of the mold.
8. A mean, dirty, paltry fellow.
9. (offensive, slang) A worker who acts against trade union policies, especially a strikebreaker.

Synonyms

• (paltry fellow): villain
• (strikebreaker): blackleg, knobstick, scalie