1805, in geology and mineralogy, "tendency (of rocks or gems) to break cleanly 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, 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;" traditionally first used in this sense by U.S. publicist Joseph I. Breen (1888-1965), head of the Production Code Administration (replaced 1945 by Eric Johnston), enforcers of Hollywood self-censorship, in reference to Jane Russell's costumes and poses in "The Outlaw."
"soldiers generally," 1757, from military (adj.); commonly only with the definite article. Earlier, "a military man" (1736).
type of fastening for clothing, 1719, originally a belt loop for carrying a weapon, of unknown origin; perhaps from Portuguese froco, from Latin floccus "tuft of wool," a word of unknown etymology.