This is the 2347th most frequent Japanese word.
ゆ
"ゆ" (yu) can mean "hot water" or "bath" in Japanese.
ゆ in this sentence refers to steam or hot water often associated with hot springs.
ゆは温泉で見られる蒸気です。
Yu is steam often seen in hot springs.
ゆ here represents medicinal hot water used traditionally for healing purposes.
昔の人々は、湯を薬として使いました。
People in ancient times used yu as medicine.
ゆ signifies the concept of warm water, distinguishing it from cold water in context.