Source : Webster's Revised Unabridged Dictionary (1913)

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}).

Source : WordNet®

Trichophyton
     n : a genus of fungus of the family Moniliaceae; causes ringworm
         and favus [syn: {genus Trichophyton}]