to become thin; to fade; to grow pale
薬が効いて痛みが薄らいだ。
The pain faded as the medicine took effect.
あの日の記憶が薄らいで、前に進めた。
With the memories of that day fading, she could finally move forward.
朝日が昇ると、湖の霧が薄らぐ。
As the morning sun rises, the fog over the lake thins out.