noun
cooled boiled water
Water that has been boiled and then allowed to cool, often used for drinking or preparing baby formula.
赤ちゃんに湯冷ましを飲ませる。
I give the baby cooled boiled water to drink.
湯冷ましを作って冷蔵庫で冷やしておく。
I make cooled boiled water and keep it chilled in the fridge.
noun
vessel for cooling hot water
A container, such as a pot or bowl, used specifically to cool boiled water. Often a wide, shallow vessel.
湯冷ましに熱湯を移して冷ます。
I pour the boiling water into a cooling vessel to let it cool.
白湯 refers to plain hot water, while 湯冷まし is boiled water that has been cooled down.
Compound of 湯 (yu, 'hot water') and 冷まし (samashi, 'cooling'), the noun form of 冷ます (samasu, 'to cool').