godan verb (-mu), intransitive verb
Describes physical slackening or loss of tension: a rope loosens, skin droops, a ceiling sags, or a stretched object becomes limp.
洗濯物を干すロープがたるんできた。
The clothesline has started to sag.
年をとると、ほおの肉がたるむ。
As you age, the flesh of your cheeks droops.
godan verb (-mu), intransitive verb
slack off; lose focus; not put one's heart in
Used for a drop in mental tension or effort: attention wanders, work becomes careless, or one's attitude becomes lax.
試合の後半で集中力がたるんでしまった。
My concentration slackened in the second half of the match.
仕事が一段落して気がたるんだ。
With work settling down, I let my guard down.