means The single fertilized cell formed when a sperm and an egg fuse, carrying a complete set of chromosomes and capable of dividing into an embryo.

from From Greek zygotos, 'yoked' or 'joined,' from zygon, 'a yoke' — the wooden crossbar that binds two oxen together. The word entered scientific English in the late 19th century, when biologists needed a name for the moment two cells become one: two halves yoked into a single new thing. The same zygon yokes itself into 'zygomatic' (the cheekbone, joining the skull) and stands as a distant cousin of Latin iugum and English 'yoke' itself.