Definition of "quadruplum" []

• In medieval music: The fourth part in polyphonic composition, counting upward from the tenor as one, usually a part duplicating the latter. (noun)
• A composition for four voices. Compare triplum. (noun)

The Century Dictionary (Public Domain)

• "The compositions remained the same as formerly, triplum, quadruplum, etc."
• "All of these forms were also distinguished as duplum, triplum and quadruplum, according to the number of voices."
• "[1914] The Ben. note quotes Ammianus Marcellinus xxvi. 6, where it is said of Petronius, father-in-law of Valens: "ad nudandos sine discretione cunctos immaniter flagrans nocentes pariter et insontes post exquisita tormenta quadrupli nexibus vinciebat, debita jam inde a temporibus principio Aureliani perscrutans, et impendio maerens si quemquam absolvisset indemnem;" and adds: "Est ergo quadruplum hoc loco non quadrimenstrua pensio, non superexactio, sed debitorum, quae soluta non fuerant, crudelis inquisitio et quadrupli poena his qui non solverant imposita.""