Synonyms of the word

mysterious

• adj. Of unknown origin.
• adj. Having unknown qualities.
• adj. Difficult to understand.
• adj. Deliberately evasive or enigmatic.

cryptic

• adj. Having hidden meaning.
• adj. Mystified or of an obscure nature.
• adj. Involving use of code or cipher/cypher.
• adj. (zoology) Well camouflaged; having good camouflage.
• adj. (biology) Apparently identical, but actually genetically distinct.
• n. (informal) A cryptic crossword.

cryptical

• adj. cryptic.

deep

• adj. (heading, of a physical distance) Extending far away from a point of reference, especially downwards.
• adj. (heading, intellectual, social) Complex, involved.
• adj. (sound, voice) Low in pitch.
• adj. (of a color) Dark and highly saturated.
• adj. (sleep) Sound, heavy (describing a state of sleep from which one is not easily awoken).
• adj. Immersed, submerged (in).
• adj. Muddy; boggy; sandy; said of roads.
• adv. Deeply.
• n. (literary, with "the") The deep part of a lake, sea, etc.
• n. (rare) A deep shade of colour.
• n. (US, rare) The profound part of a problem.
• n. (with "the") The sea, the ocean.
• n. (cricket) A fielding position near the boundary.

esoteric

• adj. intended for or likely to be understood by only a small number of people with a specialized knowledge…
• adj. Having to do with concepts that are highly theoretical and without obvious practical application; often…
• adj. Confidential; private.
• n. An esoteric doctrine or treatise; esoteric philosophy.
• n. One who believes, or is an initiate, in esoteric doctrines or rites.

incomprehensible

• adj. Impossible or very difficult to understand.

inexplicable

• adj. Impossible to explain; not easily accounted for.

inscrutable

• adj. Difficult or impossible to comprehend, fathom, or interpret.
• n. One who or that which is inscrutable; a person, etc. that cannot be comprehended.

mystic

• adj. Of, or relating to mystics, mysticism or occult mysteries; mystical.
• adj. Mysterious and strange; arcane, obscure or enigmatic.
• n. Someone who practices mysticism.

mystical

• adj. Relating to mystics or mysticism.
• adj. Having a spiritual significance that transcends human understanding.
• adj. Inspiring a sense of spiritual mystery, awe, and fascination.

mystifying

• adj. Very hard to understand; baffling.
• v. present participle of mystify.

occult

• v. (transitive, astronomy) To cover or hide from view.
• v. (transitive, rare) To dissimulate, conceal, or obfuscate.
• adj. (medicine) Secret; hidden from general knowledge; undetected.
• adj. Related to the occult; pertaining to mysticism, magic, or astrology.
• adj. Esoteric.
• n. (usually with "the") Supernatural affairs.

secret

• n. (countable, uncountable) Knowledge that is hidden and intended to be kept hidden.
• n. (uncountable) Something not understood or known.
• n. (archaic, in the plural) The genital organs.
• adj. Being or kept hidden.
• adj. (obsolete) Withdrawn from general intercourse or notice; in retirement or secrecy; secluded.
• adj. (obsolete) Faithful to a secret; not inclined to divulge or betray confidence; secretive.
• adj. (obsolete) Separate; distinct.
• v. (transitive) To make or keep secret.
• v. (transitive) To hide secretly.