Etymology
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celerity (n.)

"swiftness, rapidity of motion," late 15c., from Old French celeritee (14c., Modern French célérité), from Latin celeritatem (nominative celeritas) "swiftness," from celer "swift," from PIE *keli- "speeding" (source also of Sanskrit carati "goes," Greek keles "fast horse or ship," Lithuanian šuoliai "a gallop," Old High German scelo "stallion").

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acceleration (n.)
Origin and meaning of acceleration

"act or condition of going faster," 1530s, from Latin accelerationem (nominative acceleratio) "a hastening," noun of action from past-participle stem of accelerare "to hasten, quicken," from ad "to" (see ad-) + celerare "hasten," from celer "swift," which is perhaps from PIE *keli- "speeding" (see celerity). 

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accelerate (v.)
Origin and meaning of accelerate

1520s, "hasten the occurrence of;" 1590s, "make quicker" (implied in accelerating), from Latin acceleratus, past participle of accelerare "to hasten, quicken" (trans.), "make haste" (intrans.), from ad "to" (see ad-) + celerare "hasten," from celer "swift," which is perhaps from PIE *keli- "speeding" (see celerity). Intransitive sense of "go faster, become faster" in English is from 1640s. Related: Accelerated; accelerative.

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rapidity (n.)

"celerity of motion or action," 1650s, from French rapidité and directly from Latin rapiditatem (nominative rapiditas) "swiftness, rapidity, velocity," from rapidus "hasty, swift, rapid" (see rapid).

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haste (n.)
late 13c., "hurrying, haste; celerity, swiftness, speed;" c. 1300, "need for quick action, urgency;" from Old French haste "haste, urgency, hastiness" (12c., Modern French hâte), from Frankish *haifst "violence" or another Germanic source, from Proto-Germanic *haifstiz (source also of Gothic haifsts "strife," Old English hæste "violent, vehement, impetuous"). From late 14c. as "undue haste, rashness, unwise or unseemly quickness." To make haste "act quickly" is recorded by 1530s.
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