miosis

(noun) (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). Synonyms: meiosis, reduction division.

(noun) reflex contraction of the sphincter muscle of the iris in response to a bright light (or certain drugs) causing the pupil to become smaller. Synonyms: light reflex, pupillary reflex, myosis.