Plural of dual; pairs, or in mathematics/linguistics, forms or elements that come in twos.
From dual (noun) + -s (plural suffix). Dual as a noun is less common than as an adjective, but in mathematics and some languages, dual refers to specific grammatical or structural forms associated with the number two.
In old Latin, nouns had singular (one), plural (many), AND dual (exactly two)—most languages lost it, but ancient Sanskrit still uses duals perfectly, showing humans once carefully distinguished between 'two cows' and 'many cows.'
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