Translation guide
The English verb 'loosen' covers several distinct actions: making something physically less tight, relaxing rules or restrictions, and becoming less tense. Japanese uses different verbs depending on what is being loosened and whether the action is intentional or spontaneous.
To intentionally reduce tightness of a fastened object.
To make regulations or supervision less strict.
To relax physically or emotionally.
Transitive verb for loosening stiff muscles or tension. Often used for massage or stretching.
To break up compacted earth or similar substances.
Used for loosening soil, tangled threads, etc.
緩める (transitive) is for intentionally loosening something. 緩む (intransitive) is for something becoming loose on its own. Choose based on whether there is a deliberate agent.
彼はネジを緩めた。
He loosened the screw.
ネジが自然に緩んだ。
The screw loosened by itself.
ネジが緩んだ
The screw came loose.
Can also be used for relaxing rules or discipline, but less formal than 緩和する.
規則を緩める
loosen the rules
肩の力をほぐす
loosen up one's shoulders
Intransitive verb meaning muscles or tension loosen naturally.
緊張がほぐれた
The tension loosened.
Can describe a grip or facial expression relaxing.
表情が緩む
one's expression loosens/relaxes
土をほぐす
loosen the soil
While 緩める is a common translation, it does not work for loosening muscles or soil. Use ほぐす for those contexts.