Etymology

Noun

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.

   • 1882: Scab was the terror of the sheep farmer, and the peril of his calling. — James Edwin Thorold Rogers, A History of Agriculture and Prices in England, Volume 4, p. 306.

4. Several different diseases of potatoes producing pits and other damage on their surface, caused by Streptomyces -bacteria.
5. Short form for common scab, a relatively harmless variety of scab caused by Streptomyces scabies.
6. (founding) A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.
7. A mean, dirty, paltry fellow.
8. A worker who acts against trade union policies, especially a strikebreaker.
9. Any one of various more or less destructive fungus diseases attacking cultivated plants, and forming dark-colored crustlike spots.

Verb

1. To get covered by a scab.
2. To act as strikebreaker.
3. To beg (for), cadge, bum

   I scabbed some money off a friend.