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.

Apocalyptic \A*poc`a*lyp"tic\ ([.a]*p[o^]k`[.a]*l[i^]p"t[i^]k),
Apocalyptist \A*poc`a*lyp"tist\, n.
   The writer of the Apocalypse.

Source : WordNet®

apocalyptic
     adj 1: prophetic of devastation or ultimate doom [syn: {apocalyptical},
             {revelatory}]
     2: of or relating to an apocalypse