The 1901 Jewish Encyclopedia
In rabbinic and New Testament literature, the second department of Gehenna, the nether world; almost synonymous with Sheol (Midr. Konen; compare Joshua ben Levi in 'Er. 19a). In Revelation 9:11 Abaddon is personified as the Angel of Hell: "And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon." In the Old Testament, however, the word is peculiar tothe "Wisdom" literature, being found in Job, 28:22, 26:6, 31:12; Proverbs 15:11; Psalms 88:12. In Proverbs 27:20 the Hebrew text has Abaddoh, but the marginal reading has Abaddon.
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Singer, Isidore, Ph.D, Projector and Managing Editor. Entry for 'Abaddon'. 1901 The Jewish Encyclopedia. https://www.studylight.org/encyclopedias/eng/tje/a/abaddon.html. 1901.