Pronunciation: (dOO-al'i-tē, dyOO-), [key]
1. a dual state or quality.
2. Math.a symmetry within a mathematical system such that a theorem remains valid if certain objects, relations, or operations are interchanged, as the interchange of points and lines in a plane in projective geometry.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.