(military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors

One who secretly collects information concerning the enemies of a government or group, One who secretly collects information for a business about one or more of its competitors, a secret watcher; someone who secretly watches other people, verb_ catch sight of, secretly collect sensitive or classified information; engage in espionage, watch, observe, or inquire secretly, transitive verb_ To gain sight of; to discover at a distance, or in a state of concealment; to espy; to see, To discover by close search or examination, To explore; to view, inspect, and examine secretly, as a country; -- usually with out, intransitive verb_ To search narrowly; to scrutinize, To engage in espionage, To discover by close observation

Plural form of enemy