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The Catholic Encyclopedia
Abyss is primarily and classically an adjective, meaning deep, very deep (Wisdom 10:19; Job 38:16). Elsewhere in the Bible, and once in Diog. Laert., it is a substantive. Some thirty times in the Septuagint it is the equivalent of the Hebrew tehom, Assyrian tihamtu, and once each of the Hebrew meculah, "sea-deep", culah, "deep flood", and rachabh, "spacious place". Hence the meanings: (1) primeval waters; (2) the waters beneath the earth; (3) the upper seas and rivers; (4) the abode of the dead, limbo; (5) the abode of the evil spirits, hell. The last two meanings are the only ones found in the New Testament.
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Obstat, Nihil. Lafort, Remy, Censor. Entry for 'Abyss'. The Catholic Encyclopedia. https://www.studylight.org/encyclopedias/eng/tce/a/abyss.html. Robert Appleton Company. New York. 1914.