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 and why it is sometimes reffered to as "The Apocalypse".
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