climaxyoudaoicibaDictYouDict[climax 词源字典]
climax: [16] Etymologically, a climax is a series of steps by which a goal is achieved, but in the late 18th century English, anticipating the culmination, started using it for the goal itself. It comes, via late Latin, from Greek klimax ‘ladder’, which was ultimately from the same source (the Indo-European base *kli-) as produced English lean. This came to be used metaphorically as a rhetorical term for a figure of speech in which a series of statements is arranged in order of increasing forcefulness, and hence for any escalating progression: ‘the top of the climax of their wickedness’, Edmund Burke 1793.

Whence modern English ‘high point’.
=> ladder, lean[climax etymology, climax origin, 英语词源]
climax (n.)youdaoicibaDictYouDict
1580s, in the rhetorical sense (a chain of reasoning in graduating steps from weaker to stronger), from Late Latin climax (genitive climacis), from Greek klimax "propositions rising in effectiveness," literally "ladder," from root of klinein "to slope," from PIE root *klei- "to lean" (see lean (v.)).

The rhetorical meaning evolved in English through "series of steps by which a goal is achieved," to "escalating steps," to (1789) "high point of intensity or development," a usage credited by the OED to "popular ignorance." The meaning "sexual orgasm" is recorded by 1880 (also in terms such as climax of orgasm), said to have been promoted from c. 1900 by birth-control pioneer Marie Stopes (1880-1958) and others as a more accessible word than orgasm (n.).
climax (v.)youdaoicibaDictYouDict
1835, "to reach the highest point," from climax (n.). Related: Climaxed; climaxing.