[noun] being twofold; a classification into two opposed parts or subclasses; "the dichotomy between eastern and western culture" Synonyms: dichotomy
[noun] (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 Synonyms: wave-particle
[noun] (geometry) the interchangeability of the roles of points and planes in the theorems of projective geometry
