/ əkˌseləˈreɪʃn; NAmE / noun
1.
[ U , sing. ] acceleration (in sth) an increase in how fast sth happens :
an acceleration in the rate of economic growth
2.
[ U ] the rate at which a vehicle increases speed :
a car with good acceleration
3.
[ U ] ( physics ) the rate at which the velocity (= speed in a particular direction) of an object changes
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WORD ORIGIN
late 15th cent.: from Latin acceleratio(n-) , from accelerare hasten, from ad- towards + celer swift.