verb
-ens; -ened; -ening
to make (something) tight or tighter or to become tight or tighter [+ obj]
tighten the noose
tighten the screws
tighten up
[phrasal verb]
tighten up or tighten (something) up or tighten up (something) :to become more strict or effective or to make (something) more strict or effective
tighten your belt