1589, from L.L.
climax (gen.
climacis), from Gk.
klimax "propositions rising in effectiveness," lit. "ladder," from base of
klinein "to slope," from PIE base
*klei- "to lean" (see
lean (v.)). The rhetorical meaning evolved in Eng. through "series of steps by which a goal is achieved," to "escalating steps," to (1789) "high point," a usage credited by the OED "to popular ignorance." The verb is 1835, from the noun. The meaning "orgasm" is first recorded 1918, apparently coined by birth-control pioneer Marie Stopes, as a more accessible word than
orgasm.