an enemy or opponent
The word was found on December 7, 2014 on the online newspaper of the New York Times http://www.nytimes.com/2014/12/07/world/middleeast/hostage-luke-somers-is-killed-in-yemen-during-rescue-attempt-american-official-says.html?ref=todayspaper. The word was found on the middle of the article “America’s Special Operations forces have played a central role in global combat missions since the attacks of Sept. 11, 2001, the most notable being the raid into Pakistan in 2011 that killed Osama bin Laden. But the challenges of distance, weather, equipment failure, pinpoint intelligence — and unpredictable actions by the adversary — are ever-present.”
The word was used in the sentence to show to describe as the enemy. The word adversary is used as enemy to show the situation presented.