1. A catastrophic event; such as, the end of the world: An apocalypse is a relatively recent development in its meaning because originally it was an alternative name for the book of the Bible known as the 'Revelation of St. John'.

The term apocalypse is also defined as a cosmic cataclysm in which God destroys the ruling powers of evil which is based on a prophetic disclosure or a revelation.
2. The last book of the New Testament in the Bible which contains visionary descriptions of heaven and of conflicts between good and evil and of the end of the world; attributed to John the apostle.
3. Any of a number of anonymous Jewish or Christian texts from around the second century B.C. to the second century A.D. containing prophetic or symbolic visions; especially, of the imminent destruction of the world and the salvation of the righteous.
4. A great or total devastation; doom; such as, the apocalypse of nuclear war.
5. Etymology: "revelation, disclosure", from Catholic-Church Latin apocalypsis, "revelation"; from Greek apokalupsis, a derivative of the verb apokalyptein, "to uncover"; from apo-, "away, off" + kalyptein, "to cover, to conceal".

A compound word that refers to war, famine, pestilence or conquest, and death: The Four Horsemen are personified as the four major "plagues" or "evils" of mankind; which will come at the end of the world.

The Four Horsemen are used to describe people or other agents that can result in imminent catastrophe.