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to slacken; to loosen; to relax; to droop (e.g. loose or flabby skin); to sag (ceiling)
to slack off (e.g. one's work, attention); to not put one's heart in
長期休暇の後は気がたるんで仕事に集中しにくくなる。
After a long vacation, one's focus slackens and it becomes hard to concentrate on work.
古いロープがたるんで荷物をしっかり固定できなかった。
The old rope slackened and I couldn't secure the luggage properly.
年齢とともに頬の皮膚がたるむのは自然な老化現象である。
Sagging of the cheek skin with age is a natural aging phenomenon.