#1 quadruple v. increase fourfold; "His stock earning quadrupled". wn
#2 quadruple n. [quartet, quartette, quadruplet] a set of four similar things considered as a unit. wn
#3 quadruple s. [quadruplicate, quadruplex, fourfold, four-fold] having four units or components; "quadruple rhythm has four beats per measure"; "quadruplex wire". wn
#4 quadruple n. a quantity that is four times as great as another. wn
#5 quadruple s. [fourfold, four-fold] four times as great or many; "a fourfold increase in the dosage". wn
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