expression, ichidan verb
tighten the reins; bring under control
Idiomatic expression. Literally means to pull the reins of a horse, but often used figuratively to mean taking firm control of a situation or person.
プロジェクトの遅れが目立ってきたので、マネージャーは手綱を締めることにした。
As the project delays became noticeable, the manager decided to tighten the reins.
Parents need to bring their children's behavior under control.