the.com/cleavage

means The visible division between a woman's breasts as shown by a low neckline, or more generally, a split between two parts of something.

from From Old English 'cleofan,' meaning to split or divide, the same root that gives us 'cleave' — a wonderfully two-faced word that means both 'to split apart' and 'to cling together.' The geological sense came first (rocks cleaving along a plane), and the anatomical sense arrived later, borrowing that same idea of a visible dividing line.