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]

WordNet (r) 3.0 (2006):

quadruple time
    n 1: a time signature indicating four beats to the bar [syn:
         common time, four-four time, quadruple time, common
         measure]