1. to loosen; to slacken
手の力を少し緩める。Loosen the tension in your hands slightly.
2. to relax (attention, efforts, etc.); to let down (one's guard); to relieve (tension)
そこでようやく少女はその表情を緩めた。It was then that the girl finally relaxed her expression.
3. to relax (a rule); to ease (e.g. restrictions); to loosen (control)
学校は髪型に関する校則を緩めた。The school relaxed its rules on hairstyles.
4. to reduce (speed); to slow down; to ease up
だけどスピードは緩めない。But I won't slow down.
5. to make more gradual (of a slope)