mysterious mysterious /mɪˈstɪriːəs/

adjective

1. () Of an obscure nature  ( cryptical , deep , mystifying , cryptic , inscrutable , mysterious )
   of an obscure nature
    The new insurance policy is written without cryptic or mysterious terms
   the new insurance policy is written without cryptic or mysterious terms
    A deep dark secret
   a deep dark secret
    The inscrutable workings of Providence
   the inscrutable workings of Providence
    In its mysterious past it encompasses all the dim origins of life
   in its mysterious past it encompasses all the dim origins of life
    Rituals totally mystifying to visitors from other lands
   rituals totally mystifying to visitors from other lands
   
2. () Having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding  ( mystical , occult , orphic , mysterious , mystic , secret )
   having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding
    Mysterious symbols
   mysterious symbols
    The mystical style of Blake
   the mystical style of Blake
    Occult lore
   occult lore
    The secret learning of the ancients
   the secret learning of the ancients