The Collaborative International Dictionary of English v.0.48:

Motive \Mo"tive\, a.
   Causing motion; having power to move, or tending to move; as,
   a motive argument; motive power. "Motive faculty." --Bp.
   Wilkins.
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   Motive power (Mach.), a natural agent, as water, steam,
      wind, electricity, etc., used to impart motion to
      machinery; a motor; a mover.
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The Collaborative International Dictionary of English v.0.48:

Motive \Mo"tive\, n. [F. motif, LL. motivum, from motivus
   moving, fr. L. movere, motum, to move. See Move.]
   1. That which moves; a mover. [Obs.] --Shak.
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   2. That which incites to action; anything prompting or
      exciting to choise, or moving the will; cause; reason;
      inducement; object; motivation[2].
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            By motive, I mean the whole of that which moves,
            excites, or invites the mind to volition, whether
            that be one thing singly, or many things
            conjunctively.                        --J. Edwards.
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   3. (Mus.) The theme or subject; a leading phrase or passage
      which is reproduced and varied through the course of a
      comor a movement; a short figure, or melodic germ, out of
      which a whole movement is develpoed. See also Leading
      motive, under Leading. [Written also motivo.]
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   4. (Fine Arts) That which produces conception, invention, or
      creation in the mind of the artist in undertaking his
      subject; the guiding or controlling idea manifested in a
      work of art, or any part of one.
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   Syn: Incentive; incitement; inducement; reason; spur;
        stimulus; cause.

   Usage: Motive, Inducement, Reason. Motive is the word
          originally used in speaking of that which determines
          the choice. We call it an inducement when it is
          attractive in its nature. We call it a reason when it
          is more immediately addressed to the intellect in the
          form of argument.
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The Collaborative International Dictionary of English v.0.48:

Motive \Mo"tive\, v. t.
   To prompt or incite by a motive or motives; to move.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

135 Moby Thesaurus words for "motive":
   activating, active, actuating, aim, ambition, angle, animating,
   animus, antecedent, argument, aspiration, attraction, basis,
   burden, case, causal, causative, cause, chapter, compelling,
   concern, consideration, counsel, desideration, desideratum, design,
   desire, determinant, determination, device, directive, driving,
   effect, emotion, end, enticement, essence, feeling, figure,
   fixed purpose, focus of attention, focus of interest, function,
   gist, goad, goal, grounds, head, heading, idea, impellent,
   impelling, impulsive, in motion, incentive, incitement, inducement,
   inducive, influence, intendment, intent, intention, issue, kinetic,
   leitmotiv, living issue, lure, main point, matter, matter in hand,
   meaning, meat, mind, mobile, motif, motile, motivating,
   motivating force, motivation, motivational, motor, moving, nisus,
   object, objective, operative, passion, pattern, phrase, plan,
   point, point at issue, point in question, pressing, problem, prod,
   project, propellant, propelling, proposal, propulsive, propulsory,
   prospectus, pulsive, purpose, pushing, question, rationale, reason,
   resolution, resolve, rubric, sake, shoving, spring, spur,
   stimulation, stimulus, stirring, striving, study, subject,
   subject matter, subject of thought, substance, text, theme,
   thrusting, topic, transitional, traveling, urge, urgent, view,
   will