WordWeb Online

1. Lose velocity; move more slowly
   "The car decelerated";
   - slow, slow down, slow up, retard
    
2. Reduce the speed of
   "He decelerated the car";
   - slow down

Derived forms: decelerated, decelerating, decelerates

Type of: alter, change, decrease, diminish, fall, lessen, modify

Antonym: accelerate