The Chinese word 暗号 (ànhào), meaning "secret signal" or "password", is a compound word formed by combining two meaningful characters: 暗 (àn), which means "dark", "hidden", or "secret", and 号 (hào), which means "signal", "mark", or "number". Together, through a modifier-head structure, "暗" modifies "号" to specify the type of signal, literally a "secret signal", where the first character describes the concealed nature of the second, creating a new, unified concept for a pre-arranged covert sign used for identification or communication.