Thayer's Greek Lexicon

 Armageddon = "the hill or city of Megiddo"
1. In Rev. 16:16 the scene of the struggle of good and evil is
suggested by that battle plain of Esdraelon, which was famous for
two great victories, of Barak over the Canaanites, and of Gideon
over the Midianites; and for two great disasters, the deaths of
Saul and Josiah. Hence in Revelation a place of great slaughter,
the scene of a terrible retribution upon the wicked. The RSV
translates the name as Har-Magedon, i.e. the hill (as Ar is the
city) of Megiddo.