used bathwater; leftover bathwater
Refers to bathwater remaining in the tub after someone has bathed. Often used in contexts like reusing water for laundry or describing water that has cooled.
Doing laundry with leftover bathwater saves water.
By morning, the leftover bathwater had gone completely cold.
Compound of 残り (nokori, 'remaining') + 湯 (yu, 'hot water').