mystery

noun
  1. Something that is difficult or impossible to understand or explain. noun
    The cause of the strange noise remains a mystery.
    The disappearance of the ancient civilization is one of history's great mysteries.
  2. A genre of fiction that involves a mysterious death or a crime to be solved. noun
    She enjoys reading mystery novels before bed.
    The movie is a gripping mystery that keeps you guessing until the end.
  3. A religious truth that one can know only by revelation and cannot fully understand. noun
    The concept of the Holy Trinity is considered a mystery in Christian theology.
    The mysteries of faith are often contemplated by theologians.