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
hold the fort
to cope in an emergency, to act as a temporary substitute
The assistant has been holding the fort at his company while his boss is on vacation.
