An enigma often takes the form of providing descriptive attributes but leaving to the audience to guess what it is that could have those attributes (which are sometimes apparently contradictory):
Rain is spent.
Now colors bent
Frame a clear, blue sky.
[answer: a rainbow]

Enigma also occurs when tropes are used in series, each of which is fairly clear, but their combined effect teases with its obscurity. In this example, periphrasis (or antonomasia) is employed repeatedly to bring about enigma:
Elizabeth Taylor, twice Cleopatra to her Anthony, never quite reconciled her Marilyn Monroe with her Scarlett O'Hara.

• paradox
• metaphor
• Figures that obscure or conceal meaning:
  • noema
  • schematismus
  • allegory