Learner's definition of TIGHTEN
to make (something) tight or tighter or to become tight or tighter
tighten the noose
tighten the screws
tighten (something) up
tighten up (something)
to become more strict or effective or to make (something) more strict or effective
Security around the building has tightened up recently.
They tightened up security around the building.
We installed new machines to tighten up the assembly line.
tighten your belt