Not allowed to be revealed, hidden, occult.

Obscure, esoteric, mysterious; = mystical, adj. 2.

More generally: mysterious, enigmatic, obscure, esoteric; of hidden meaning or nature; having an unknown or mysterious origin or influence. Cf. mystic…

Hidden from view or knowledge; concealed; kept secret. Frequently in to keep (something) dark: to keep (something) concealed; to keep secret.

Hidden, concealed, secret.

Not apprehended, or not apprehensible, by the mind; beyond ordinary understanding or knowledge; abstruse, mysterious; inexplicable.

transferred and figurative. Unsubstantial, fleeting; figurative, mystical.

Concealed, hidden; secret. Obsolete.

= cryptic, adj. 2.

The quality or condition of being obscure or enigmatic; mysteriousness. Also: mysteries collectively.

Full of or fraught with mystery; shrouded in mystery; hidden from human knowledge or understanding; difficult or impossible to explain, solve, or…

Mysterious. In early use: †mystical (obsolete).

Secret, concealed; occult, mystical. Also: cryptographic.

Recondite, abstruse. Cf. recherché, adj. Obsolete. rare.

In extended use: refined, subtle; elevated, exalted; select, esoteric.

Of arcane character; mysterious, dim.

Resembling (that of) the Sphinx; esp. enigmatical, mysterious, inscrutable, insoluble.

characteristic of the Sphinx; enigmatical, mysterious.

= abstruse, adj.

Sphinx-like; characteristic of a Sphinx; enigmatic, inscrutable.