What is the origin of celerity?
Celerity, “swiftness; speed,” comes via Middle French célérité from Latin celeritās (inflectional stem celeritāt-) “swiftness, quickness, speed,” a derivative of the adjective celer. Celer comes from the Proto-Indo-European root kel– “to drive, incite to quick motion” and the suffix –es– (Old Latin keles– regularly changes to Classical Latin celer-). The Latin adjective celeber, also celebris “busy, crowded, frequented” (source of English celebrate, celebrated) is also formed from kel-. The root also appears in Greek kélēs “runner, racer, racehorse, fast ship.” Celerity entered English in the second half of the 15th century.