expression, ichidan verb
loosen the reins; let up on someone
Literally means to slacken the reins of a horse. Figuratively, it means to relax control or pressure on someone, giving them more freedom or easing strictness.
上司は部下への手綱を緩めて、自主性を尊重することにした。
The boss decided to loosen the reins on his subordinates and respect their autonomy.
親が子供への手綱を緩めすぎると、規律が失われることもある。
If parents let up on their children too much, discipline can sometimes be lost.