The Collaborative International Dictionary of English v.0.48:

Triple \Tri"ple\, v. i. [imp. & p. p. Tripled; p. pr. & vb. n.
   Tripling.] [Cf. F. tripler. See Triple, a.]
   To make threefold, or thrice as much or as many; to treble;
   as, to triple the tax on coffee.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Triple \Tri"ple\, a. [L. triplus; tri- (see Tri-) + -plus, as
   in duplus double: cf. F. triple. See Double, and cf.
   Treble.]
   1. Consisting of three united; multiplied by three;
      threefold; as, a triple knot; a triple tie.
      [1913 Webster]

            By thy triple shape as thou art seen. --Dryden.
      [1913 Webster]

   2. Three times repeated; treble. See Treble.
      [1913 Webster]

   3. One of three; third. [Obs.] --Shak.
      [1913 Webster]

   Triple crown, the crown, or tiara, of the pope. See
      Tiara, 2.

   Triple-expansion steam engine, a compound steam engine in
      which the same steam performs work in three cylinders
      successively.

   Triple measure (Mus.), a measure of tree beats of which
      first only is accented.

   Triple ratio (Math.), a ratio which is equal to 3.

   Triple salt (Chem.), a salt containing three distinct basic
      atoms as radicals; thus, microcosmic salt is a triple
      salt.

   Triple star (Astron.), a system of three stars in close
      proximity.

   Triple time (Mus.), that time in which each measure is
      divided into three equal parts.

   Triple valve, in an automatic air brake for railroad cars,
      the valve under each car, by means of which the brake is
      controlled by a change of pressure in the air pipe leading
      from the locomotive.
      [1913 Webster]

WordNet (r) 3.0 (2006):

triple
    adj 1: having three units or components or elements; "a ternary
           operation"; "a treble row of red beads"; "overcrowding
           made triple sessions necessary"; "triple time has three
           beats per measure"; "triplex windows" [syn: ternary,
           treble, triple, triplex]
    2: three times as great or many; "a claim for treble (or triple)
       damages"; "a threefold increase" [syn: treble, threefold,
       three-fold, triple]
    n 1: a base hit at which the batter stops safely at third base
         [syn: triple, three-base hit, three-bagger]
    2: a set of three similar things considered as a unit [syn:
       trio, triad, triplet, triple]
    3: a quantity that is three times as great as another
    v 1: increase threefold; "Triple your income!" [syn: triple,
         treble]
    2: hit a three-base hit

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "triple":
   accelerate, aggravate, beef up, blow up, complicate, concentrate,
   condense, consolidate, cube, deepen, deltoid, double, enhance,
   exacerbate, exaggerate, fan-shaped, heat up, heighten, hop up,
   hot up, intensify, jazz up, key up, magnify, make complex,
   multiply by three, ramify, redouble, reinforce, sharpen, soup up,
   step up, strengthen, tern, ternal, ternary, ternate, three,
   three-in-one, three-ply, threefold, threesome, treble, triadic,
   trial, triangular, trilogic, trinal, trine, trinity, trio, triplex,
   triplicate, triumvirate, triune, troika, whet