The Collaborative International Dictionary of English v.0.48:

Accelerate \Ac*cel"er*ate\, v. t. [imp. & p. p. Accelerated;
   p. pr. & vb. n. Accelerating.] [L. acceleratus, p. p. of
   accelerare; ad + celerare to hasten; celer quick. See
   Celerity.]
   1. To cause to move faster; to quicken the motion of; to add
      to the speed of; -- opposed to retard.
      [1913 Webster]

   2. To quicken the natural or ordinary progression or process
      of; as, to accelerate the growth of a plant, the increase
      of wealth, etc.
      [1913 Webster]

   3. To hasten, as the occurence of an event; as, to accelerate
      our departure.
      [1913 Webster]

   Accelerated motion (Mech.), motion with a continually
      increasing velocity.

   Accelerating force, the force which causes accelerated
      motion.                                     --Nichol.
      [1913 Webster]

   Syn: To hasten; expedite; quicken; dispatch; forward;
        advance; further.
        [1913 Webster]

WordNet (r) 3.0 (2006):

accelerate
    v 1: move faster; "The car accelerated" [syn: accelerate,
         speed up, speed, quicken] [ant: decelerate,
         retard, slow, slow down, slow up]
    2: cause to move faster; "He accelerated the car" [syn:
       accelerate, speed, speed up] [ant: decelerate, slow
       down]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "accelerate":
   activate, aggravate, atomize, beef up, blow up, bombard, bundle,
   bustle, cleave, complicate, concentrate, condense, consolidate,
   crack on, cross-bombard, crowd, deepen, dispatch, double, drive,
   drive on, enhance, exacerbate, exaggerate, expedite, fission,
   forward, gain ground, get going, haste, hasten, hasten on, heat up,
   heighten, hie on, hop up, hot up, hurry, hurry along, hurry on,
   hurry up, hustle, hustle up, impel, intensify, jazz up, key up,
   magnify, make complex, nucleize, open the throttle, pick up speed,
   precipitate, press, push, push on, push through, put on,
   put on steam, quicken, race, railroad through, ramify, redouble,
   reinforce, rev, rush, rush along, shake up, sharpen,
   smash the atom, soup up, speed, speed along, speed up, spur,
   stampede, step on it, step up, strengthen, triple, urge, whet,
   whip, whip along