Synonyms for Mysterious:

adj.

complex (adjective)
complicated, involved, convoluted, difficult, abstruse, obscure, perplexing, intricate, complex, puzzling.
deep (adjective)
orphic.
difficult (adjective)
involved.
magical (adjective)
magical.
secret (adjective)
mystic.
secret, concealed (adjective)
secretive, occult, puzzling, strange, insoluble, baffling, inexplicable, unknown, esoteric, abstruse, enigmatic, arcane, cryptic, obscure, unfathomable, perplexing, transcendental, incomprehensible, magical, spiritual, inscrutable, mystical, mystifying, difficult, unnatural, oracular.
uncertain (adjective)
controversial, questionable, changeable, debatable, moot, confused, uncertain, deniable, disputable, arguable, unsure, undecided, ambivalent, unconvinced, contestable, precarious, vague, insecure, tentative.
unintelligible (adjective)
confusing, baffling, unclear, unreadable, illegible, indecipherable, enigmatic, cryptic, mystifying.

n.

elaborate, contorted. ineffable, magic, spiritual, anonymous, magical, transcendental, personal, oracular, unknown, arcane, unfathomable, numinous, strange. ambiguous, secretive, in strict confidence, classified. knowledge, explain. mysterious (noun)
deep, esoteric, mystical, cryptic, incomprehensible, occult, mystic, inscrutable, secret, cryptical, orphic, inexplicable, mystifying.
puzzling (noun)
insoluble, unaccountable, unnatural, strange.

Other synonyms:

arcane, secretive, classified, strange, anonymous. personal. inexpressible
ineffable.
insolvable
insoluble.
occult
magic, magical, occult.
profound
unfathomable.
prophetic
oracular.
strange
unaccountable.

Usage examples for mysterious

  1. By what mysterious force was he driven? – The Outcaste by F. E. Penny
  2. But cannot you be a little less mysterious – Malcolm Sage, Detective by Herbert George Jenkins