Primarily and classically an adjective, very deep

Catholic Encyclopedia. . 2006.

     Catholic_Encyclopedia Abyss
    (Greek abyssos).
    Abyss is primarily and classically an adjective, meaning deep, very deep (Wisd., x, 19; Job, xxxviii, 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.
    A.J. MAAS
    Transcribed by Stephen Patrick Wilson Dedicated to Paul James Wilson

The Catholic Encyclopedia, Volume VIII. — New York: Robert Appleton Company. . 1910.

Catholic encyclopedia.