The Collaborative International Dictionary of English v.0.48:

Compel \Com*pel"\, v. t. [imp. & p. p. Compelled; p. pr. & vb.
   n. Compelling.] [L. compellere, compulsum, to drive
   together, to compel, urge; com- + pellere to drive: cf. OF.
   compellir. See Pulse.]
   1. To drive or urge with force, or irresistibly; to force; to
      constrain; to oblige; to necessitate, either by physical
      or moral force.
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            Wolsey . . . compelled the people to pay up the
            whole subsidy at once.                --Hallam.
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            And they compel one Simon . . . to bear his cross.
                                                  --Mark xv. 21.
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   2. To take by force or violence; to seize; to exact; to
      extort. [R.]
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            Commissions, which compel from each
            The sixth part of his substance.      --Shak.
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   3. To force to yield; to overpower; to subjugate.
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            Easy sleep their weary limbs compelled. --Dryden.
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            I compel all creatures to my will.    --Tennyson.
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   4. To gather or unite in a crowd or company. [A Latinism] "In
      one troop compelled." --Dryden.
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   5. To call forth; to summon. [Obs.] --Chapman.
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            She had this knight from far compelled. --Spenser.

   Syn: To force; constrain; oblige; necessitate; coerce. See
        Coerce.
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WordNet (r) 3.0 (2006):

compelling
    adj 1: driving or forcing; "compelling ambition"
    2: tending to persuade by forcefulness of argument; "new and
       compelling evidence"

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "compelling":
   actuating, acute, animating, causal, causative, clamorous,
   coactive, compulsive, compulsory, constraining, critical, crucial,
   crying, decretal, decretive, decretory, dictating, directive,
   driving, exigent, gripping, high-pressure, high-priority, holding,
   impelling, imperative, imperious, impulsive, inducive, insistent,
   instant, instructive, irresistible, jussive, mandating, motivating,
   motivational, motive, moving, obligating, obsessing, obsessional,
   obsessive, peremptory, pivotal, possessing, preceptive,
   preoccupying, prescriptive, pressing, restraining, urgent