Same word as obscure:

abstruse, ambiguous, arcane, clear as mud, complicated, concealed, confusing, cryptic, dark, deep, dim, doubtful, enigmatic, enigmatical, esoteric, far-out, hazy, hidden, illegible, illogical, impenetrable, incomprehensible, inconceivable, incredible, indecisive, indefinite, indeterminate, indistinct, inexplicable, inscrutable, insoluble, intricate, involved, mysterious, occult, opaque, recondite, unaccountable, unbelievable, unclear, undefined, unfathomable, unintelligible, vague