That cannot be easily understood; completely obscure or mysterious; unfathomable; enigmatic.
The definition of inscrutable is someone or something that is hard to figure out, understand or interpret.
An example of an inscrutable problem is one for which no solution can be quickly found.
Difficult to understand or interpret; impenetrable.
One who or that which is inscrutable; a person, etc. that cannot be comprehended.
Origin of inscrutable
From American Heritage Dictionary of the English Language, 5th Edition