The Collaborative International Dictionary of English v.0.48:

Triplicate \Trip"li*cate\, a. [L. triplicatus, p. p. of
   triplicare to triple, treble; tri- (see Tri-) + plicare to
   fold. See Ply, v. t.]
   Made thrice as much; threefold; tripled.
   [1913 Webster]

   Triplicate ratio (Math.), the ratio of the cubes of two
      quantities; thus, the triplicate ratio of a to b is a^3:
      b^3.
      [1913 Webster]