Definition of "opponency" [op•po•nen•cy]

• The act of opening an academic disputation; the proposition of objections to a tenet, as an exercise for a degree. (noun)

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• "L (1992) The color hexagon: a chromaticity diagram based on photoreceptor excitations as a generalized representation of colour opponency."
• "Researchers have long regarded color opponency to be hardwired in the brain, completely forbidding perception of reddish green or yellowish blue."
• "Under special circumstances, though, people can see the "forbidden" colors, suggesting that color opponency in the brain has a softwired stage that can be disabled."