early 15c., "diverse condition;" c. 1600 "act of diverting," from Middle French diversion, from Late Latin diversionem (nominative diversio), noun of action from past participle stem of Latin divertere (see divert).
Sense of "amusement, entertainment" is first recorded 1640s. Hence, divertimento (1823), from the Italian form; originally "a musical composition designed primarily for entertainment."[diversion etymology, diversion origin, 英语词源]