of depth; not capable of being sounded or measured
abysmal, abyssal, unfathomable(adj)
resembling an abyss in depth; so deep as to be unmeasurable
"the abyssal depths of the ocean"
impossible to come to understand
impossible to fathom or understand; incomprehensible
The sheer numbers they attacked with were unfathomable.
difficult to penetrate.
Chambers 20th Century Dictionary
un-fath′om-a-bl, adj. that cannot be fathomed, too deep to be measured or to be understood.—n. Unfath′omableness.—adv. Unfath′omably.—adj. Unfath′omed, not sounded.
The numerical value of unfathomable in Chaldean Numerology is: 6
The numerical value of unfathomable in Pythagorean Numerology is: 1