Meaning

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 anim

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

originFrom Ancient Greek μύω (múō, “to close the eyes”) + English -osis.

Etymology from Wiktionary, CC BY-SA 3.0