Source : Webster's Revised Unabridged Dictionary (1913)

Double \Dou"ble\, v. t. [imp. & p. p. {Doubled}; p. pr. & vb. n.
   {Doubling}.] [OE. doblen, dublen, doublen, F. doubler, fr. L.
   duplare, fr. duplus. See {Double}, a.]
   1. To increase by adding an equal number, quantity, length,
      value, or the like; multiply by two; to double a sum of
      money; to double a number, or length.

            Double six thousand, and then treble that. --Shak.

   2. To make of two thicknesses or folds by turning or bending
      together in the middle; to fold one part upon another part
      of; as, to double the leaf of a book, and the like; to
      clinch, as the fist; -- often followed by up; as, to
      double up a sheet of paper or cloth.

Source : WordNet®

doubled
     adj 1: twice as great or many; "ate a double portion"; "the dose is
            doubled"; "a twofold increase" [syn: {double}, {twofold}]
     2: folded in two; "doubled sheets of paper"