WordWeb Online

1. The act of making something tighter
   "the tightening of economic controls"

1. Make tight or tighter
   "Tighten the wire";
   - fasten
    
2. Become tight or tighter
   "The rope tightened"
    
3. (of laws or regulations) make more restrictive, or impose greater penalties
   "tighten the rules";
   - stiffen, tighten up, constrain
    
4. Narrow or limit
   "tighten the influx of foreigners";
   - reduce

Derived forms: tightenings

Type of: adjustment, alter, alteration, bound, change, confine, limit, modification, modify, restrict, throttle, trammel

Antonym: loosening