WordNet (r) 3.0 (2006):

miosis
    n 1: (genetics) cell division that produces reproductive cells
         in sexually reproducing organisms; the nucleus divides into
         four nuclei each containing half the chromosome number
         (leading to gametes in animals and spores in plants) [syn:
         meiosis, miosis, reduction division]
    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, myosis]