The Collaborative International Dictionary of English v.0.48:

Quadruple \Quad"ru*ple\, a. [L. quadruplus, from quattuor four:
   cf. F. quadruple. See Quadrate, and cf. Double.]
   Fourfold; as, to make quadruple restitution; a quadruple
   alliance.
   [1913 Webster]

   Quadruple time (Mus.), that in which each measure is
      divided into four equal parts.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quadruple \Quad"ru*ple\, n. [Cf. F. quadruple, L. quadruplum.]
   four times the sum or number; a fourfold amount; as, to
   receive to quadruple of the amount in damages.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quadruple \Quad"ru*ple\, v. t. [imp. & p. p. Quadrupled; p.
   pr. & vb. n. Quadrupling.] [L. quadruplare: cf. F.
   quadrupler.]
   To multiply by four; to increase fourfold; to double; to
   double twice. --A. Smith.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Quadruple \Quad"ru*ple\, v. i.
   To be multiplied by four; to increase fourfold; to become
   four times as much.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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