cleavage

Concise Oxford English Dictionary © 2008 Oxford University Press:
cleavage/ˈkliːvɪʤ/

▶noun

• 1 a marked difference or division between people.

• 2 the cleft between a woman's breasts.

• 3 Biology cell division, especially of a fertilized egg cell.

• 4 the splitting of rocks or crystals in a preferred plane or direction.