n.
1.being twofold
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
3.(geometry) the interchangeability of the roles of points and planes in the theorems of projective geometry
Idiom of the Day
hang by a thread/hair
to be in doubt, to depend on a very small thing
The outcome of the election was hanging by a thread until late at night.