decelerate \decelerate\ v. i.

1. 1 to reduce speed; as, The car decelerated. Opposite of accelerate.

Syn: slow, slow down, slow up, retard. [WordNet 1.5]

Source: The Collaborative International Dictionary of English v.0.48
 

decelerate \decelerate\ v. t. to cause to reduce speed. Opposite of accelerate.

Syn: slow down. [WordNet 1.5]

Source: The Collaborative International Dictionary of English v.0.48
 

decelerate

Source: WordNet (r) 2.0