noun
pouring hot water over oneself before entering the bath; pre-bath rinse
A customary practice at public baths and hot springs: scooping and pouring hot water over the body to cleanse and warm up before entering the shared tub.
温泉では、まず掛け湯をしてから湯船に入りましょう。
At a hot spring, first pour hot water over yourself before getting into the bath.
掛け湯をしないで浴槽に入るのはマナー違反です。
Entering the bathtub without doing the pre-bath rinse is bad manners.
noun
repeated pouring of hot water over oneself as a hot-spring cure
A therapeutic practice at certain hot springs where one repeatedly pours hot spring water over the body, often as part of a traditional cure regimen.
この温泉地では、古くから掛け湯による湯治が行われている。
In this hot-spring area, a cure by repeatedly pouring hot water over oneself has been practiced since old times.
Compound of 掛け (kake, 'pouring') + 湯 (yu, 'hot water'). The exact historical derivation is uncertain, but the term directly describes the action.