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.
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            Thus re["e]nforced, against the adverse fleet,
            Still doubling ours, brave Rupert leads the way.
                                                  --Dryden.
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   4. To pass around or by; to march or sail round, so as to
      reverse the direction of motion.
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            Sailing along the coast, the doubled the promontory
            of Carthage.                          --Knolles.
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   5. (Mil.) To unite, as ranks or files, so as to form one from
      each two.
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The Collaborative International Dictionary of English v.0.48:

Doubling \Dou"bling\, n.
   1. The act of one that doubles; a making double;
      reduplication; also, that which is doubled.
      [1913 Webster]

   2. A turning and winding; as, the doubling of a hunted hare;
      shift; trick; artifice. --Dryden.
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   3. (Her.) The lining of the mantle borne about the shield or
      escutcheon.
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   4. The process of redistilling spirits, to improve the
      strength and flavor.
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   5. raising the stakes in a game, such as a card game or
      backgammon, by a factor of 2.

   Syn: double.
        [WordNet 1.5]

   Doubling a cape, promontory, etc. (Naut.), sailing around
      or passing beyond a cape, promontory, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

doubling
    n 1: increase by a factor of two; "doubling with a computer took
         no time at all"
    2: raising the stakes in a card game by a factor of 2; "I
       decided his double was a bluff" [syn: doubling, double]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "doubling":
   Janus, ambiguity, ambivalence, biformity, bifurcation, bush,
   bushing, conduplication, conjugation, copying, crease, creasing,
   crimp, dichotomy, dog-ear, double, doubleness, doublethink,
   doublure, dualism, duality, duplexity, duplicate, duplication,
   duplicature, duplicity, echo, equivocality, facing, filler,
   filling, flection, flexure, flounce, fold, frill, gather,
   gemination, halving, imitation, ingemination, inlay, inlayer,
   insole, interlineation, irony, iteration, lapel, lappet, liner,
   lining, packing, padding, pairing, plagiarism, plica, plication,
   plicature, ply, polarity, quotation, reappearance, rebirth,
   recurrence, redoubling, reduplication, reecho, regurgitation,
   reincarnation, reiteration, renewal, reoccurrence, repetition,
   replication, reproduction, resumption, return, ruche, ruching,
   ruffle, stuffing, tuck, twinning, two-facedness, twoness, wadding,
   wainscot