Duality is the ability to see opposites in equal relationship to each other, not separated, as illustrated in this diagram.
In the Cosmic Equation, duality becomes trialectic, as A becomes A and not-A in a primary-secondary relationship that unifies the either-or approach of Aristotelian logic and the ‘No-mind’ way of life, as exemplified in Advaita, Tao, and Zen.
About 1385 ‘twofold nature’, from Old French dualité, from Late Latin duālitātem (nominative duālitās), from Latin duālis ‘that contains two’, from duo ‘two’, from Greek duo ‘two, both’, from PIE base *dwo- ‘two’.