Definition of scab

• n. - An incrustation over a sore, wound, vesicle, or pustule, formed by the drying up of the discharge from the diseased part.
• n. - The itch in man; also, the scurvy.
• n. - The mange, esp. when it appears on sheep.
• n. - A disease of potatoes producing pits in their surface, caused by a minute fungus (Tiburcinia Scabies).
• n. - A slight irregular protuberance which defaces the surface of a casting, caused by the breaking away of a part of the mold.
• n. - A mean, dirty, paltry fellow.
• n. - 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.
• v. i. - To become covered with a scab; as, the wound scabbed over.