Source : Webster's Revised Unabridged Dictionary (1913)

Duplicate \Du"pli*cate\, n.
   1. That which exactly resembles or corresponds to something
      else; another, correspondent to the first; hence, a copy;
      a transcript; a counterpart.

            I send a duplicate both of it and my last dispatch.
                                                  -- Sir W.
                                                  Temple.

   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.

Duplicate \Du"pli*cate\, v. t. [imp. & p. p. {Duplicated}; p.
   pr. & vb. n. {Duplicating}.]
   1. To double; to fold; to render double.

   2. To make a duplicate of (something); to make a copy or
      transcript of. --Glanvill.

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

Duplicate \Du"pli*cate\, a. [L. duplicatus, p. p. of duplicare
   to double, fr. duplex double, twofold. See {Duplex}.]
   Double; twofold.

   {Duplicate proportion} or {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.

Source : WordNet®

duplicate
     adj 1: identically copied from an original; "a duplicate key"
     2: being two identical [syn: {matching}, {twin(a)}, {twinned}]
     n 1: something additional of the same kind; "he always carried
          extras in case of an emergency" [syn: {extra}]
     2: a copy that corresponds to an original exactly; "he made a
        duplicate for the files" [syn: {duplication}]
     v 1: make or do or perform again; "He could never replicate his
          brilliant performance of the magic trick" [syn: {reduplicate},
           {double}, {repeat}, {replicate}]
     2: duplicate or match; "The polished surface twinned his face
        and chest in reverse" [syn: {twin}, {parallel}]
     3: make a duplicate or duplicates of; "Could you please
        duplicate this letter for me?"
     4: increase twofold; "The population doubled within 50 years"
        [syn: {double}]