noun

the practice of spying or of using spies, typically by governments to obtain political and military information.

the camouflage and secrecy of espionage

spying,undercover work,cloak-and-dagger activities,surveillance,reconnaissance,intelligence,eavesdropping,infiltration,cyberespionage,counter-espionage,counter-intelligence,ninjutsu,bugging,wiretapping,recon