n. 1. That which exactly resembles or corresponds to something else; another, correspondent to the first; hence, a copy; a transcript; a counterpart. [ 1913 Webster ]

I send a duplicate both of it and my last dispatch. Sir W. Temple. [ 1913 Webster ]

2. (Law) An original instrument repeated; a document which is the same as another in all essential particulars, and differing from a mere copy in having all the validity of an original. Burrill. [ 1913 Webster ]

v. t. [ imp. & p. p. Duplicated p. pr. & vb. n. Duplicating. ] 1. To double; to fold; to render double. [ 1913 Webster ]

2. To make a duplicate of (something); to make a copy or transcript of. Glanvill. [ 1913 Webster ]

3. (Biol.) To divide into two by natural growth or spontaneous action; as, infusoria duplicate themselves. [ 1913 Webster ]

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 ]