Source : Webster's Revised Unabridged Dictionary (1913)

Myosis \My*o"sis\, n. [NL., fr. Gr. ? to close the eyes or
   lips.] (Med.)
   Long-continued contraction of the pupil of the eye.

Source : WordNet®

myosis
     n 1: an acute infectious disease occurring in epidemic form and
          featuring paroxysms of pain (usually in the chest) [syn:
           {epidemic pleurodynia}, {epidemic myalgia}, {diaphragmatic
          pleurisy}, {Bornholm disease}]
     2: reflex contraction of the sphincter muscle of the iris in
        response to a bright light (or certain drugs) causing the
        pupil to become smaller [syn: {light reflex}, {pupillary
        reflex}, {miosis}]
     [also: {myoses} (pl)]