Meaning

noun two items of the same kind

originFrom Ancient Greek δυάς (duás), δυάδ- (duád-) from δύο (dúo, “two”), from Proto-Indo-European *duwó, *duwéh₃ (*dwóh₁). The mathematics sense was coined by American scientist Josiah Willard Gibbs in 1884 in the second half of his book Elements of Vector Analysis.

Etymology from Wiktionary, CC BY-SA 3.0