A riddle is a puzzling question or problem; a conundrum. The term is most often used in connection with problems expressed in words, obscure matters that can be clarified only by a guess: "Plutarch wrote that Homer died of worry and chagrin because he could not solve a certain riddle." "Oedipus solved the riddle of the Sphinx by revealing that the person described was man, who 'walked' on four legs, then two, then three." A puzzle is a toy or other device designed to amuse by presenting a difficulty that can be solved through effort or ingenuity: "He works the crossword puzzle every morning that it appears in his newspaper." An enigma is a baffling problem or question that contains an air or atmosphere of mystery: "Zach concluded that his former wife would always be an enigma to him." In a radio broadcast early during World War II, Winston Churchill said: "I cannot forecast to you the action of Russia. It is a riddle wrapped in a mystery inside an enigma."
Dictionary of problem words and expressions. Harry Shaw. 1975.