The word "溶洞" is formed by combining the character "溶", meaning to dissolve, which uses the water radical (氵) to indicate its relation to liquid and the component "容" for phonetic approximation, with the character "洞", meaning cave, which also incorporates the water radical (氵) to associate it with water and the component "同" for sound. Together, the compound literally denotes a water-formed cave through dissolution, specifically referring to a limestone cave created by water eroding rock.