If you describe something or someone as an enigma, you mean they are mysterious or difficult to understand. Iran remains an enigma for the outside world. = mystery. someone or something that is strange and difficult to understand = mystery (aenigma, from , from ainos ). Device used by the German military to encode strategic messages before and during World War II. The Enigma code was first broken by the Poles in the early 1930s, so that German messages were eventually intercepted and deciphered by Allied code-breakers during the war. (See also Ultra.)