The Collaborative International Dictionary of English v.0.48:

Revelation \Rev`e*la"tion\, n. [F. r['e]v['e]lation, L.
   revelatio. See Reveal.]
   1. The act of revealing, disclosing, or discovering to others
      what was before unknown to them.
      [1913 Webster]

   2. That which is revealed.
      [1913 Webster]

   3. (Theol.)
      (a) The act of revealing divine truth.
      (b) That which is revealed by God to man; esp., the Bible.
          [1913 Webster]

                By revelation he made known unto me the mystery,
                as I wrote afore in few words.    --Eph. iii. 3.
          [1913 Webster]

   4. Specifically, the last book of the sacred canon,
      containing the prophecies of St. John; the Apocalypse or
      Book of Revelation or The Revelation of Saint John.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Apocalypse \A*poc"a*lypse\, n. [L. apocalypsis, Gr. ?, fr. ? to
   uncover, to disclose; ? from + ? to cover, conceal: cf. F.
   apocalypse.]
   1. (Eccl.) One of a numerous class of writings proceeding
      from Jewish authors between 250 b. c. and 150 a. d., and
      designed to propagate the Jewish faith or to cheer the
      hearts of the Jewish people with the promise of
      deliverance and glory; or proceeding from Christian
      authors of the opening centuries and designed to portray
      the future.
      [Webster 1913 Suppl.]

   2. Specifically, the revelation delivered to St. John, in the
      isle of Patmos, near the close of the first century,
      forming the last book of the New Testament (called
      Revelation or the Apocalypse).
      [1913 Webster]

   3. Anything viewed as a revelation, especially one that is
      highly significant for the person receiving it; a
      disclosure. Often used of a realization or revelation that
      changes a person's goals or style of life.
      [1913 Webster +PJC]

            The new apocalypse of Nature.         --Carlyle.
      [1913 Webster]

   4. the final battle between good and evil, as foreseen in
      Saint John's Apocalypse; the time when God conquers the
      powers of evil, attended by cataclysmic cosmic events, and
      sometimes thought of as the end of the world; an
      Armageddon.
      [PJC] Apocalyptic

WordNet (r) 3.0 (2006):

apocalypse
    n 1: a cosmic cataclysm in which God destroys the ruling powers
         of evil
    2: the last book of the New Testament; contains visionary
       descriptions of heaven and of conflicts between good and evil
       and of the end of the world; attributed to Saint John the
       Apostle [syn: Revelation, Revelation of Saint John the
       Divine, Apocalypse, Book of Revelation]

Moby Thesaurus II by Grady Ward, 1.0:

72 Moby Thesaurus words for "apocalypse":
   actuarial prediction, afflatus, baring, direct communication,
   disclosing, disclosure, discovering, discovery, divine inspiration,
   divine revelation, envisioning, epiphany, expose, exposition,
   exposure, foreboding, forecast, forecasting, foreshowing,
   foresight, foretelling, guesswork, improbability, inspiration,
   laying bare, manifestation, mystical experience, mysticism, omen,
   oracle, patefaction, precognition, prediction, prefiguration,
   prefigurement, prefiguring, presage, presaging, presentiment,
   preshowing, presignifying, prevision, probability, prognosis,
   prognostication, promise, prophecy, prophesying, prospectus,
   removing the veil, revealing, revealment, revelation, showing up,
   showup, soothsay, speculation, statistical prediction, stripping,
   theophania, theophany, theopneustia, theopneusty, uncloaking,
   uncovering, unfolding, unfoldment, unmasking, unveiling,
   unwrapping, vaticination, vision



Easton's 1897 Bible Dictionary:

Apocalypse
   the Greek name of the Book of Revelation (q.v.).


Hitchcock's Bible Names Dictionary (late 1800's):

Apocalypse, uncovering, revelation