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):

impel
    v 1: urge or force (a person) to an action; constrain or
         motivate [syn: impel, force]
    2: cause to move forward with force; "Steam propels this ship"
       [syn: propel, impel]

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "impel":
   actuate, advance, animate, beset, bind, bowl, bunt, butt, cause,
   cause to, compel, constrain, drive, drive on, energize, enforce,
   foment, force, forward, foster, galvanize, give an impetus,
   give momentum, goad, grip, have, hold, incite, infatuate, inspire,
   instigate, make, mobilize, motivate, move, move to action,
   not let go, nudge, obsess, pedal, pole, possess, power, preoccupy,
   promote, propel, push, put in motion, restrain, roll, row,
   set agoing, set going, set in motion, shove, shunt, spark, spur,
   stimulate, sweep, sweep along, thrust, tie, treadle, troll,
   trundle, use force upon, whip on