unfathomable

/ənˈfæðəməbəl/

/ənˈfæðəməbəl/

Other forms: unfathomably

Unfathomable means impossible to ever understand. For most people, the field of quantum mechanics is unfathomable.

Fathoms are seafaring units of measure equaling about six feet. So something that is unfathomable is also immeasurable, especially when it comes to depth. If your sonar isn't bouncing anything back to you, you're dealing with an unfathomable distance. Metaphorically, unfathomable can refer to something that resembles an abyss, some figurative notion that's so deep you can't even measure it.

Definitions of unfathomable

1. adjective

   impossible to come to understand
   synonyms:

   incomprehensible, uncomprehensible

   difficult to understand
2. adjective

   of depth; not capable of being sounded or measured
   synonyms:

   deep

   having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination

   unsoundable

   too deep to determine the depth of

   antonyms:

   fathomable

   (of depth) capable of being sounded or measured for depth
3. adjective

   resembling an abyss in depth; so deep as to be unmeasurable
   synonyms: abysmal, abyssal

   deep

   having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination