1 a person or group actively opposing or hostile to another, or to a cause etc.
2 a a hostile nation or army, esp. in war. b a member of this. c a hostile ship or aircraft.
3 (usu. foll. by of, to) an adversary or opponent.
4 a thing that harms or injures.
5 (attrib.) of or belonging to an enemy (destroyed by enemy action).
Etymology: ME f. OF enemi f. L inimicus (as IN-(1), amicus friend)
Useful english dictionary. 2012.