This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. Swiftness of action or motion; speed. See Synonyms at haste.

n. Speed.

n. The speed of individual waves (as opposed to the speed of groups of waves).

n. Rapidity of motion; quickness; swiftness.

n. Rapidity of motion; swiftness; quickness; speed.

n. Velocity, Swiftness, etc. See quickness.

n. a rate that is rapid

"Second, he used the word celerity in conversation."

pace    rate   

promptitude    instantaneousness    expedition    immediacy    instancy    fleetness    expeditiousness    promptness    dispatch    despatch   

quickness    swiftness    rapidity   

Solidarity    Verity    barbarity    clarity    dexterity    disparity    familiarity    hilarity    irregularity    parity   

rapidity    promptitude    alacrity    agility    punctuality    fluency    thoroughness    clearness    steadiness    distinctness