What does cleavage mean?
Cleavage refers to a clean split or division along a natural plane of weakness. Its oldest and most technical use is in mineralogy and geology, where it describes how crystals and rocks break along smooth, regular surfaces — mica and diamond being classic examples. Biology borrowed the term for embryonic cleavage, the series of rapid cell divisions by which a fertilized egg develops into a multicellular embryo. In everyday language, however, cleavage most often means the visible hollow between a woman's breasts created by a low-cut neckline, a sense that arose in the twentieth century and gives the word a distinctly sensual connotation in fashion contexts. The word derives from the verb 'to cleave', meaning to split or cut apart, via the noun-forming suffix '-age'. Because it spans three unrelated-seeming domains — geology, embryology, and dress — cleavage is a striking example of a single English word serving both laboratory terminology and casual conversation.
A split or division along a natural plane of weakness, especially in minerals, rocks, or crystals.
"Diamond has perfect cleavage in four directions, which allows it to be split before faceting."
Primarily used in geology, mineralogy, and materials science.
The repeated mitotic division of a fertilized egg into progressively smaller cells during early embryonic development.
"Cleavage begins within hours of fertilization and produces a ball of cells called a morula."
The visible hollow between a woman's breasts as accentuated by a low-cut garment.
"The gown was designed with a plunging neckline that revealed considerable cleavage."
Informal register; carries a sensual connotation.
The plural appears chiefly in scientific writing, where different types or directions of cleavage in minerals or embryos are discussed.
"The mineral exhibits two distinct cleavages at right angles to each other."
The same word that describes how diamonds split along perfect planes also names the effect of a low-cut dress — one vocabulary item, two very different dinner conversations.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cleavage
Cleavage derives from the Old English verb clēofan, meaning 'to split or cut apart', which shares a common Germanic ancestry with related forms such as 'cloven' and 'cleft'. The suffix '-age', borrowed from French, was added to form a noun denoting the act or result of splitting. The geological sense developed first, followed by the biological sense describing early cell division, while the fashion sense referring to the space between the breasts emerged much later, in the twentieth century.
Related word forms
How cleavage is actually used
In geology and mineralogy the term is technical and neutral; in fashion contexts it carries a distinctly sensual connotation and is used almost exclusively about women's clothing. The embryology sense is strictly scientific.
Easily confused with cleavage
A crevice is a natural narrow crack in a surface, whereas cleavage specifically denotes a clean split along a plane of structural weakness, especially in minerals or cells.