late 15c., from Old French celeritee (14c., Modern French célérité), from Latin celeritatem (nominative celeritas) "swiftness," from celer "swift," from possible PIE root *kel- "to drive, set in swift motion" (cognates: Sanskrit carati "goes," Greek keles "fast horse or ship," keleuthos "journey, road," Lithuanian sulys "a gallop," Old High German scelo "stallion").