"tighten" in the verb sense
1. tighten, fasten
make tight or tighter
"Tighten the wire"
2. tighten
become tight or tighter
"The rope tightened"
3. stiffen, tighten, tighten up, constrain
severely restrict in scope or extent
"tighten the rules"
"stiffen the regulations"
4. reduce, tighten
narrow or limit
"reduce the influx of foreigners"
Source: WordNet® (An amazing lexical database of English)
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