noun
A somewhat literary or elegant term for a hot spring, often used in travel writing or traditional inn names.
山奥のいで湯に浸かると、日頃の疲れが癒される。
Soaking in a hot spring deep in the mountains heals everyday fatigue.
温泉 is the standard, everyday word for a hot spring. いで湯 is more literary and evocative, often used in poetic or promotional contexts.
From 出で (ide, the 連用形 of classical verb 出づ 'to come out') + 湯 (yu, 'hot water'), literally 'gushing hot water'. The spelling いで湯 is a common modern representation.