Verbs

(v)tighten, fastenmake tight or tighter“Tighten the wire”
(v)tightenbecome tight or tighter“The rope tightened”
(v)stiffen, tighten, tighten up, constrainseverely restrict in scope or extent“tighten the rules”, “stiffen the regulations”
(v)reduce, tightennarrow or limit“reduce the influx of foreigners”