The word "十八" (shíbā), meaning "eighteen", is formed through a straightforward numerical compounding process common in Chinese. It combines the character "十" (shí), which means "ten", with the character "八" (bā), meaning "eight". The structure follows a logical additive principle where the first digit denotes the base (ten) and the second digit specifies the added units (eight), resulting in the combined value of eighteen. This decimal-based, left-to-right compositional method is characteristic of how Chinese forms numbers from eleven to ninety-nine.