- cleavage (n.)
- 1816, in geology, "action of splitting (rocks or gems) along natural fissures," from cleave (v.1) + -age. General meaning "action or state of cleaving or being cleft" is from 1867. The sense of "cleft between a woman's breasts in low-cut clothing" is first recorded 1946, when it was defined in a "Time" magazine article [Aug. 5] as the "Johnston Office trade term for the shadowed depression dividing an actress' bosom into two distinct sections."