INSCRUTABLE
cryptic, cryptical, deep, inscrutable, mysterious, mystifying
(adjective) of an obscure nature; “the new insurance policy is written without cryptic or mysterious terms”; “a deep dark secret”; “the inscrutable workings of Providence”; “in its mysterious past it encompasses all the dim origins of life”- Rachel Carson; “rituals totally mystifying to visitors from other lands”
Source: WordNet® 3.1
Etymology
Adjective
inscrutable (comparative more inscrutable, superlative most inscrutable)
Difficult or impossible to comprehend, fathom, or interpret.
Synonyms: ineffable, Thesaurus:incomprehensible
Noun
inscrutable (plural inscrutables)
One who or that which is inscrutable; a person, etc. that cannot be comprehended.
Source: Wiktionary
In*scru"ta*ble, a. Etym: [L. inscrutabilis : cf. F. inscrutable. See
In- not, and Scrutiny.]
Definition: Unsearchable; incapable of being searched into and understood
by inquiry or study; impossible or difficult to be explained or
accounted for satisfactorily; obscure; incomprehensible; as, an
inscrutable design or event.
'T is not in man To yield a reason for the will of Heaven Which is
inscrutable. Beau. & Fl.
Waiving a question so inscrutable as this. De Quincey.
Source: Webster’s Unabridged Dictionary 1913 Edition