From Greek 'ainigma' (a riddle), from 'ainos' (a tale) — entered English via Saint Paul's use in 1 Corinthians 13:12.
A person or thing that is mysterious, puzzling, or difficult to understand.
From Latin 'aenigma' (a riddle), from Greek 'ainigma' (αἴνιγμα, a riddle, an obscure saying), from 'ainissesthai' (αἰνίσσεσθαι, to speak in riddles, to speak obliquely), from 'ainos' (αἶνος, a tale, a fable, a saying), possibly from PIE *h₂ey-no- (a significant utterance). The Greek word was used to describe anything expressed obscurely or figuratively. Saint Paul used it memorably in 1 Corinthians 13:12 — 'we see through a glass darkly' — where the Greek reads 'en ainigmati' (ἐν αἰνίγματι, in a riddle, enigmatically), suggesting that mortal
The most famous modern use of the word is the Enigma machine — the German cipher device in World War II whose code-breaking by Alan Turing at Bletchley Park is estimated to have shortened the war by two years. Turing's team called the project 'Ultra,' but the machine's name 'Enigma' (chosen by its German inventor Arthur Scherbius in the 1920s) perfectly captured the Greek meaning: a riddle wrapped in mechanical complexity.