Abaddon

n. hell; Apollyon (angel of hell)

Abaddon (Hebrew אבדון Avaddon, meaning "destruction"). In Biblical poetry (Job 26:6; Proverbs 15:11), it comes to mean "place of destruction", or the realm of the dead, and is associated with Sheol. Abaddon is also one of the compartments of Gehenna. By extension, it can mean an underworld abode of lost souls, or hell.
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(n.)
The destroyer, or angel of the bottomless pit; -- the same as Apollyon and Asmodeus.
  

(n.)
Hell; the bottomless pit.
  

[Other] In medieval myth the synonym for Hell and/or the ruler thereof, and in Revelations 9:7-11 it is the Christian angel of Hell. The Hebrew word abaddon means "place of destruction" (Job 26:8 and Psalm 88:11). Prior to its corruption by the Judeo-Christian tradition, "Abaddon" referred to the pit or cave that was used in mystery religions and schools as a rite of passage into the greater mysteries. Often, the experience would entail the use of ritual substances that put the aspirant into an altered state in which he or she could receive divine revelation. Because the experience was sometimes unpleasant, this rite came to be viewed as being "hellish." However, it was considered absolutely necessary so that the seeker may become pure enough to encounter the "mind of God."

Abaddon 'abaddon (Hebrew) [from the verbal root 'abad to perish, be cut off] Destruction, abyss; the region of the dead, synonym of She'ol in the Old Testament. Equivalent to the Greek apollyon (destruction, laying waste -- Rev 9:11). Thus Abaddon, Apollyon, Hades, and Orcus all signify the underworld -- the kama-loka or region of disintegrating "shells," human or other.