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 (kwŏ-dro͞o′pəl, -drŭp′əl, kwŏd′ro͝o-pəl)
1. Consisting of four parts or members.
2. Four times as much in size, strength, number, or amount.
3. Music Having four beats to the measure.
A fourfold amount or number.
tr. & intr.v. quad·ru·pled, quad·ru·pling, quad·ru·ples
To multiply or be multiplied by four: quadrupled the order; quadrupled in size.

[From Middle English quadriple, fourfold amount, and quadruple, tooth with four roots, both from Old French quadruple, from Latin quadruplum, from neuter of quadruplus, fourfold : quadru-, quadri-, quadri- + -plus, -fold; see pel- in Indo-European roots.]

quad·ru′ply adv.
References in classic literature ?
All crimes against the state, are punished here with the utmost severity; but, if the person accused makes his innocence plainly to appear upon his trial, the accuser is immediately put to an ignominious death; and out of his goods or lands the innocent person is quadruply recompensed for the loss of his time, for the danger he underwent, for the hardship of his imprisonment, and for all the charges he has been at in making his defence; or, if that fund be deficient, it is largely supplied by the crown.
In Niggle's Parish, "As you walked, new distances opened out; so that you now had doubled, treble, and quadruple distances, doubly, trebly, and quadruply enchanting" ("Niggle" 114).
In 2013, Google chairman Eric Schmidt said that changes to international tax laws may result for international companies to be taxed doubly or even quadruply.
However, Schmidt refused Milliband's criticism of Google's tax situation as he said that his chief concerns about changes in the tax system might make Google to be 'doubly or quadruply taxed'.
It turns out that these dynamical symmetries provide an appropriate framework for the description of low-energy collective motions of real nuclei with certain shape symmetries: The U(5) limit corresponds to spherical nuclei, the SU(3) and SU(3)* limits to axially symmetric nuclei with quadruple deformation (prolate and oblate shapes) and the O(6) and O(6)* limits to quadruply deformed nuclei that are unstable against the axial symmetry breaking.