scab

noun

1. a crust that forms over a sore or wound during healing
2. a mangy skin disease, as scabies, of animals, esp. sheep
3. 1. any of various plant diseases characterized by roughened, scablike spots on leaves, stems, or fruits
   2. any such spot
4. : often a term of contempt or derision
   1. Slang a low, contemptible fellow; scoundrel
   2. ☆ a worker who refuses to join a union, or who works for lower wages or under different conditions than those accepted by the union
   3. a worker who refuses to strike, or who takes the place of a striking worker

intransitive verb scabbed, scabbing

1. to become covered with a scab; form a scab
2. ☆ to work or act as a scab