The Collaborative International Dictionary of English v.0.48:

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; as, to double a sum
      of money; to double a number, or length.
      [1913 Webster]

            Double six thousand, and then treble that. --Shak.
      [1913 Webster]

   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. --Prior.
      [1913 Webster]

            Then the old man
            Was wroth, and doubled up his hands.  --Tennyson.
      [1913 Webster]

   3. To be the double of; to exceed by twofold; to contain or
      be worth twice as much as.
      [1913 Webster]

            Thus re["e]nforced, against the adverse fleet,
            Still doubling ours, brave Rupert leads the way.
                                                  --Dryden.
      [1913 Webster]

   4. To pass around or by; to march or sail round, so as to
      reverse the direction of motion.
      [1913 Webster]

            Sailing along the coast, the doubled the promontory
            of Carthage.                          --Knolles.
      [1913 Webster]

   5. (Mil.) To unite, as ranks or files, so as to form one from
      each two.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

doubled \doubled\ adj.
   1. rendered twice as great or twice as many.

   Syn: double, duplex, twofold, diploid.
        [WordNet 1.5]

   2. folded in two; as, doubled sheets of paper.

   Syn: doubled over.
        [WordNet 1.5] Double dealer

WordNet (r) 3.0 (2006):

doubled
    adj 1: twice as great or many; "ate a double portion"; "the dose
           is doubled"; "a twofold increase" [syn: double,
           doubled, twofold, two-fold]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "doubled":
   creased, crimped, dog-eared, duplicated, echoed, flexible,
   flounced, fluted, foldable, folded, folding, gathered, plagiarized,
   plaited, pleated, pliable, plicate, plicated, plicatile, quilled,
   quoted, rechauffe, redoubled, reduplicated, reechoed, regurgitated,
   reiterate, reiterated, repeated, reproduced, retold, ruffled,
   tucked, twice-told, twilled, warmed up