v. i. 1. 1 to reduce speed; as, The car decelerated. Opposite of accelerate. Syn. -- slow, slow down, slow up, retard. [ WordNet 1.5 ]
v. t. to cause to reduce speed. Opposite of accelerate. Syn. -- slow down. [ WordNet 1.5 ]
n. a decrease in velocity. Opposite of acceleration Syn. -- slowing, retardation. [ WordNet 1.5 ]