duality

American  

[doo-al-i-tee, dyoo-] / duˈæl ɪ ti, dyu- /

noun

1. a dual state or quality.

2. Mathematics. 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.

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duality British  

/ djuːˈælɪtɪ /

noun

1. the state or quality of being two or in two parts; dichotomy

2. physics the principle that a wave-particle duality exists in microphysics in which wave theory and corpuscular theory are complementary. The propagation of electromagnetic radiation is analysed using wave theory but its interaction with matter is described in terms of photons. The condition of particles such as electrons, neutrons, and atoms is described in terms of de Broglie waves

3. geometry the interchangeability of the roles of the point and the plane in statements and theorems in projective geometry

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Other Word Forms

• nonduality noun

Etymology

Origin of duality

1350–1400; Middle English dualitie < Late Latin duālitās. See dual, -ity

Explanation

As hinted at by the word "dual" within it, duality refers to having two parts, often with opposite meanings, like the duality of good and evil. If there are two sides to a coin, metaphorically speaking, there's a duality. Peace and war, love and hate, up and down, and black and white are dualities. Another term for a duality is a dichotomy. Duality has technical meanings in geometry and physics. In geometry, duality refers to how points and planes have interchangeable roles in projective geometry. In physics, duality is the property of matter and electromagnetic radiation to be understood best through wave theory or particle theory.

Example Sentences

Conscious feelings are one of its techniques, emerging “deep in the subcortical regions” where the brain’s interoceptive neurons receive messages from the body and Cartesian duality dissolves.

From The Wall Street Journal • Mar. 15, 2026

But Redick knows there’s a “wonderful duality to Austin.”

From Los Angeles Times • Mar. 15, 2026

"The double protagonist angle really is a feature that lets us explore the duality of the characters, but also the storyline and the different horror approaches," Nakanishi adds.

From BBC • Feb. 27, 2026

The new duality, Li says, involves materials that can behave as both conductors and insulators.

From Science Daily • Nov. 9, 2025

One was the so- called wave-particle duality of nature at the infinitesimal scale: experiments sometimes showed light and electrons behaving like particles, and other times as waves.

From "Big Science" by Michael Hiltzik

Related Words

• artifice
• chicanery
• deceit
• dishonesty
• falsehood
• hypocrisy