The Collaborative International Dictionary of English v.0.48:

Impel \Im*pel"\, v. t. [imp. & p. p. Impelled; p. pr. & vb. n.
   Impelling.] [L. impellere; pref. im- in + pellere, pulsum,
   to drive. See Pulse a beat, and cf. Impulse.]
   To drive or urge forward or on; to press on; to incite to
   action or motion in any way.
   [1913 Webster]

         The surge impelled me on a craggy coast. --Pope.

   Syn: To instigate; incite; induce; influence; force; drive;
        urge; actuate; move.
        [1913 Webster]

WordNet (r) 3.0 (2006):

impelling
    adj 1: markedly effective as if by emotional pressure;
           "impelling skill as a teller of tales"; "an impelling
           personality"

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "impelling":
   active, actuating, animating, causal, causative, compelling,
   compulsive, directive, driving, gripping, holding, impellent,
   impulsive, in motion, inducive, mobile, motile, motivating,
   motivational, motive, motor, moving, obsessing, obsessional,
   obsessive, possessing, preoccupying, pressing, propellant,
   propelling, pulsive, stirring, thrusting, transitional, traveling,
   urgent