Source : Webster's Revised Unabridged Dictionary (1913)

Abaddon \A*bad"don\ ([.a]*b[a^]d"d[u^]n), n. [Heb. [=a]badd[=o]n
   destruction, abyss, fr. [=a]bad to be lost, to perish.]
   1. The destroyer, or angel of the bottomless pit; -- the same
      as Apollyon and Asmodeus.

   2. Hell; the bottomless pit. [Poetic]

            In all her gates, Abaddon rues Thy bold attempt.
                                                  --Milton.