Espionage (6)
I believe the answer is:
spying
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">espionage</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that espionage can be written as spying)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for spying that I've seen before include "Keeping furtive watch" , "Acting as a secret agent" , "Activity undertaken by Blunt and Philby" , "Catching sight of; agent's job" , "Engaging in espionage" .)