Source : Webster's Revised Unabridged Dictionary (1913)

Espionage \Es"pi*o*nage\ (?; 277), n. [F. espionnage, fr.
   espionner to spy, fr. espion spy, OF. espie. See {Espy}.]
   The practice or employment of spies; the practice of watching
   the words and conduct of others, to make discoveries, as
   spies or secret emissaries; secret watching.

Source : WordNet®

espionage
     n : the systematic use of spies to get military or political
         secrets