Source : Webster's Revised Unabridged Dictionary (1913)

Apocalyptic \A*poc`a*lyp"tic\, Apocalyptical
\A*poc`a*lyp"tic*al\, a. [Gr. ?.]
   Of or pertaining to a revelation, or, specifically, to the
   Revelation of St. John; containing, or of the nature of, a
   prophetic revelation.

   {Apocalyptic number}, the number 666, mentioned in --Rev.
      xiii. 18. It has been variously interpreted.