Adjective

1. abysmal, immeasurable (vs. measurable), unmeasurable, immensurable, unmeasured

usage: very great; limitless; "abysmal misery"; "abysmal stupidity"

2. abysmal, abyssal, unfathomable, deep (vs. shallow)

usage: resembling an abyss in depth; so deep as to be unmeasurable; "the abyssal depths of the ocean"

See also: abysmal (Dictionary)