Apocalypse (n): 1.the Book of Revelation (last book of the New Testament), and events described in that book. The book is marked by pseudonymity, symbolic imagery, and the expectation of an imminent cosmic cataclysm in which God destroys the ruling powers of evil and raises the righteous to life in a messianic kingdom.
2. Therefore, the more common meaning, derived from above, is a great disaster/catastrophe/end of the world.
His book tells of an environmental apocalypse.
<the fear that the next global pandemic could be an apocalypse of biblical proportions>
As an adjective: "Nobody listened to her apocalyptic predictions."
Middle English, revelation, Revelation, from Anglo-French apocalipse, from Late Latin apocalypsis, from Greek apokalypsis, from apokalyptein to uncover, from apo- + kalyptein to cover