1. a writer of apocalyptic literature.
  2. a person who adheres to the teachings of apocalyptic literature concerning the signs and events preceding the end of the world.
  3. a person who holds to any teachings that predict a catastrophic end to the world.

Origin of apocalyptist

First recorded in 1825–35; apocalypt(ic) + -ist
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018