The Collaborative International Dictionary of English v.0.48:

Abysmal \A*bys"mal\, a.
   Pertaining to, or resembling, an abyss; bottomless; unending;
   profound.
   [1913 Webster]

         Geology gives one the same abysmal extent of time that
         astronomy does of space.                 --Carlyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

abysmal
    adj 1: very great; limitless; "abysmal misery"; "abysmal
           stupidity"
    2: resembling an abyss in depth; so deep as to be unmeasurable;
       "the abyssal depths of the ocean" [syn: abysmal, abyssal,
       unfathomable]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "abysmal":
   Atlantean, Brobdingnagian, Cyclopean, Gargantuan, Herculean,
   Homeric, abyssal, appalling, astronomic, awful, bottomless,
   cavernous, colossal, deep as hell, dreadful, elephantine, enormous,
   epic, fathomless, gaping, giant, giantlike, gigantic, heroic, huge,
   illimitable, immense, infinite, jumbo, mammoth, mighty, monster,
   monstrous, monumental, mountainous, plumbless, plunging,
   prodigious, profound, soundless, stupendous, terrible, titanic,
   towering, tremendous, unfathomable, unfathomed, unsounded, vast,
   without bottom, yawning