(n.) A principal enemy. Specifically, Satan, the grand adversary of mankind.
Example Sentences:
(1) Being "plugged in" also meant that when Freud spoke out against Fox News within the pages of the liberal archenemy of the US rightwing media, the New York Times, his wife emailed Roger Ailes, the combative head of the business.
(2) America's current archenemy, al-Qaida, is not a competitor in the space race, and Chinese, Indian and European ambitions have not evoked fear of militarised space among the US public.