Source : Webster's Revised Unabridged Dictionary (1913)

Semeiology \Se`mei*ol"o*gy\, or Semiology \Se`mi*ol"o*gy\, n.
   [Gr. shmei^on a mark, a sign + -logy.]
   The science or art of signs. Specifically:
   (a) (Med.) The science of the signs or symptoms of disease;
       symptomatology.
   (b) The art of using signs in signaling.