**The Collaborative International Dictionary of English v.0.48:**

duplicate \du"pli*cate\, a. [L. duplicatus, p. p. of duplicare
to double, fr. duplex double, twofold. See Duplex.]
Double; twofold.
[1913 Webster]
Duplicate proportion or Duplicate ratio (Math.), the
proportion or ratio of squares. Thus, in geometrical
proportion, the first term to the third is said to be in a
duplicate ratio of the first to the second, or as its
square is to the square of the second. Thus, in 2, 4, 8,
16, the ratio of 2 to 8 is a duplicate of that of 2 to 4,
or as the square of 2 is to the square of 4.
[1913 Webster]