n. An incrusted substance, dry and rough, formed over a sore in healing.n. The mange, or some mangy disease caused by the presence of a parasite, as an itch-insect; scabies.n. A mean, paltry, or shabby fellow: a term of contempt.n. Specifically, in recent use, a workman who is not or refuses to become a member of a labor-union, who refuses to join in a strike, or who takes the place of a striker: an opprobrious term used by the workmen or others who dislike his action.n. In botany, a fungous disease affecting various fruits, especially apples and pears, in which a black mold appears, often distorting or destroying the fruit.n. In founding, any projection on a casting caused by a defect in the sand-mold.Having to do with “scabs,” or made by them: used opprobriously: as, scab mills; scab labor; scab shoes.To form a scab or scabby incrustation; become covered with a scab or scabs; specifically, to heal over; cicatrize; repair solution of continuity of a surface by the formation of a new skin or cicatrix.