noun
one difficulty; one danger
Often used in the set phrase 一難去ってまた一難 (one difficulty leaves, another comes), describing a series of troubles.
一難去ってまた一難、今度は車が故障した。
One trouble after another—now the car broke down.
やっと問題が解決したと思ったら
Just when I thought the problem was solved, another difficulty arose.