|Easton's Bible Dictionary|
Occurs only in Revelation 16:16 (R.V., "Har-Magedon"), as symbolically designating the place where the "battle of that great day of God Almighty" (ver. 14) shall be fought. The word properly means the "mount of Megiddo." It is the scene of the final conflict between Christ and Antichrist. The idea of such a scene was suggested by the Old Testament great battle-field, the plain of Esdraelon (q.v.).
Int. Standard Bible Encyclopedia
ar-ma-ged'-on Armageddon: Revelation 16:16; the Revised Version (British and American) "HAR-MAGEDON") (which see).
Armageddon (1 Occurrence)
Revelation 16:16 And he gathered them together into a place called in the Hebrew tongue Armageddon. (KJV BBE WBS YLT NIV)