du·al·i·ty /duˈæləti ||dju-/
  二元性
  duality
  對偶性
  duality
  自偶性
  duality
  對偶性
  Du·al·i·ty n.  The quality or condition of being two or twofold; dual character or usage.
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  duality
       n 1: being twofold; a classification into two opposed parts or
            subclasses; "the dichotomy between eastern and western
            culture" [syn: dichotomy]
       2: (physics) the property of matter and electromagnetic
          radiation that is characterized by the fact that some
          properties can be explained best by wave theory and others
          by particle theory [syn: wave-particle duality]
       3: (geometry) the interchangeability of the roles of points and
          planes in the theorems of projective geometry