sex: [14] Sex comes via Old French sexe from Latin sexus. This has traditionally been explained as a relative of Latin secāre ‘cut’ (source of English section, sector, etc), as if it denoted etymologically that ‘section’ of the population which is male or female, but that view is no longer generally held. The use of sex for ‘sexual intercourse’ (first recorded in the works of D H Lawrence) and the derivative sexy are both 20th-century developments. [sex etymology, sex origin, 英语词源]