unfathomable
1. [ adjective ] of depth; not capable of being sounded or measured
Related terms: fathomable unsoundable deep
2. [ adjective ] so deep as to be unmeasurable; unfathomable
Synonyms: abyssal abysmal
Examples:

"the abyssal depths of the ocean"

Related terms: deep
3. [ adjective ] of meaning; not capable of being penetrated
Synonyms: fathomless
Examples:

"a philosophy complex and, to the ordinary thinker, quite fathomless" "unfathomable theories"

Related terms: fathomable incomprehensible bottomless inexplicable esoteric incomprehensible
Similar spelling:   unfathomed
  unbeatable
  unavoidable