WordWeb Online

1. A pause during which things are calm or activities are diminished
   "there was never a letup in the noise";
   - lull

1. Become less in amount or intensity
   "The rain let up after a few hours";
   - abate, slack off, slack, die away
    
2. Reduce pressure or intensity
   "he let up the gas pedal and the car slowed down";
   - ease up, ease off

Derived forms: lets up, let up, letting up, letups

Type of: alter, break, change, decrease, diminish, fall, intermission, interruption, lessen, modify, pause, suspension