Antonyms of enigma:
answer, axiom, explanation, proposition, solution.
Examples of usage:
  1. He whirled on his heels and strode to the enigma of Egypt.
    "When Egypt Went Broke", Holman Day.
  2. Her face was an enigma, for it inspired everyone with the warmest sympathy, and yet if you examined it attentively there was not one beautiful feature; she could not be called handsome, but no one could have thought her ugly.
    "The Memoires of Casanova, Complete The Rare Unabridged London Edition Of 1894, plus An Unpublished Chapter of History, By Arthur Symons", Jacques Casanova de Seingalt.
  3. Human nature is an insoluble enigma, if this world is its only field.
    "Expositions of Holy Scripture: Romans Corinthians (To II Corinthians, Chap. V)", Alexander Maclaren.