Armageddon, mentioned in Book of Revelation, became synonymous with the final battle between good and evil. But what is the real meaning of this word?

By definition

1. a surprising and previously unknown fact, especially one that is made known in a dramatic way."revelations about his personal life"synonyms:disclosure, surprising fact, announcement, report; More
2. the divine or supernatural disclosure to humans of something relating to human existence or the world.

In the context or application, it refers to knowledge that God revealed to Jesus about the end times and Jesus told it to an Angel and instructed the Angel to in turn relay the information to John who wrote it down…. Revelation 1:1–3