1. Cause to proceed more slowly
   "The heavy traffic slowed up our journey";
   - slow, slow down
    
2. Lose velocity; move more slowly
   "The car slowed up";
   - decelerate, slow, slow down, retard
    
3. Become slow or slower
   "Production slowed up";
   - slow, slow down, slack, slacken

Derived forms: slowing up, slowed up, slows up

Type of: come down, decrease, dent, diminish, fall, go down, lessen, sink, weaken