Ringworm \Ring"worm"\, n. (Med.) A contagious affection of the skin due to the presence of a vegetable parasite, and forming ring-shaped discolored patches covered with vesicles or powdery scales. It occurs either on the body, the face, or the scalp. Different varieties are distinguished as {Tinea circinata}, {Tinea tonsurans}, etc., but all are caused by the same parasite (a species of {Trichophyton}).