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

Derived forms: decelerates, decelerating, decelerated

Type of: alter, change, come down, decrease, dent, diminish, fall, go down, lessen, modify, sink

Antonym: accelerate