Synonyms of the word

mystifying

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

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.

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.

mysterious

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