The word 地牢 (dìláo), meaning "dungeon", is a semantically transparent compound noun formed by combining the character 地 (dì), meaning "ground" or "earth", with 牢 (láo), meaning "prison" or "enclosure". It follows a standard modifier-head structure in Chinese word formation, where the first element 地 ("underground") specifies the location or type of the second element 牢 ("prison"), thus creating the literal and intuitive meaning of an "underground prison". This logical construction is typical of many Chinese compounds, where two meaningful characters are joined to produce a new, readily understood concept.