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1. Become quiet or quieter
   - hush, quiet, quiesce, quiet down, pipe down
    
2. Make calm or still
   "quieten the dragons of worry and fear";
   - calm, calm down, quiet, tranquilize [N. Amer], tranquillize, tranquillise [Brit], lull, still
    
3. Cause to be quiet or not talk
   "Please quieten the children in the church!";
   - hush, silence, still, shut up, hush up

Derived forms: quietening, quietens, quietened

Type of: change intensity, comfort, conquer, console, curb, inhibit, solace, soothe, stamp down, subdue, suppress

Antonym: louden