The word 密探 (mìtàn) is a compound noun formed by combining two characters: 密 (mì), meaning "secret", "confidential", or "closely-packed", and 探 (tàn), meaning "to explore", "to investigate", or "a scout". Together, they create a semantic unit where 密 modifies 探, specifying the type of "investigator" as one who operates in secrecy. Thus, the term literally means a "secret investigator" or "secret scout", and by standard usage, it translates to "secret agent", "spy", or "undercover detective". This structure follows a common Chinese word-formation pattern where an adjective-like element (密) precedes and describes a noun-like element (探) to form a new, more specific concept.