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The word "Apocalypse" comes from the Greek: ἀποκάλυψις apokalupsis
Apokalupsis means to reveal or a revelation. So in Revelation 1:1 when John says: The Revelation of Jesus Christ, which God gave unto him the word "revelation" is the word, in the original Greek, apokalupsis. That's how the book of "Revelation" got its name.
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