The Collaborative International Dictionary of English v.0.48:

Motivate \Mo"ti*vate\, v. t. [imp. & p. p. -vated; p. pr. &
   vb. n. -vating.] [From Motive, n.]
   To provide with a motive; to move; impel; induce; incite. --
   Mo`ti*va"tion, n. --William James.

   Syn: move, prompt, incite, induce impel, drive.
        [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

motivation \motivation\ n.
   1. The act or process of motivating.
      [PJC]

   2. The mental process that arouses an organism to action; as,
      a large part of a teacher's job is to give students the
      motivation to learn on their own.

   Syn: motive, need.
        [WordNet 1.5 +PJC]

   3. The goal or mental image of a goal that creates a
      motivation[2]; as, the image of a peaceful world is a
      powerful motivation for only a rare few individuals.
      [PJC]

WordNet (r) 3.0 (2006):

motivation
    n 1: the psychological feature that arouses an organism to
         action toward a desired goal; the reason for the action;
         that which gives purpose and direction to behavior; "we did
         not understand his motivation"; "he acted with the best of
         motives" [syn: motivation, motive, need]
    2: the condition of being motivated; "his motivation was at a
       high level"
    3: the act of motivating; providing incentive [syn:
       motivation, motivating]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "motivation":
   activity, actuation, animation, aptitude, aptness, brightness,
   catalyst, cleverness, direction, docility, dynamics, educability,
   facility, going, impetus, impressionability, impulse, incentive,
   incitation, incitement, influence, inner-direction, instigation,
   intelligence, kinematics, kinesipathy, kinesis, kinesitherapy,
   kinetics, malleability, mobilization, moldability, motion, move,
   movement, moving, other-direction, plasticity, pliability,
   prompting, quickness, readiness, receptivity, restlessness,
   running, spur, stimulant, stimulation, stir, stirring,
   susceptibility, teachability, teachableness, trainableness, unrest,
   velocity, willingness