The word "温泉" is formed by directly combining two meaningful characters: "温", which means "warm", and "泉", which means "spring" or "fountain". Together, they create a transparent, descriptive compound where the first character modifies the second, literally painting a picture of a "warm spring" to denote a natural geothermally heated pool of water. It is a straightforward conceptual fusion where the core meaning arises from the sum of its visually and semantically clear parts.