Source : Webster's Revised Unabridged Dictionary (1913)

Abysm \A*bysm"\, n. [OF. abisme; F. abime, LL. abyssimus, a
   superl. of L. abyssus; Gr. ?. See {Abyss}.]
   An abyss; a gulf. ``The abysm of hell.'' --Shak.

Source : WordNet®

abysm
     n : a bottomless gulf or pit; any unfathomable (or apparently
         unfathomable) cavity or chasm or void extending below
         (often used figuratively) [syn: {abyss}]