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 [informal], slack, die away
    
2. Reduce pressure or intensity
   "The rain finally let up in the afternoon";
   - ease up, ease off

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

Type of: alter, break, change, come down, decrease, dent, diminish, fall, go down, intermission, interruption, lessen, modify, pause, sink, suspension