Source : Webster's Revised Unabridged Dictionary (1913)

Compulsion \Com*pul"sion\, n. [L. compulsio. See {Compel}.]
   The act of compelling, or the state of being compelled; the
   act of driving or urging by force or by physical or moral
   constraint; subjection to force.

         If reasons were as plentiful as blackberries, I would
         give no man a reason upon compulsion.    --Shak.

         With what compulsion and laborious flight We sunk thus
         low.                                     --Milton.

   Syn: See {Constraint}.

Source : WordNet®

compulsion
     n 1: an urge to do or say something that might be better left
          undone or unsaid [syn: {irresistible impulse}]
     2: an irrational motive for performing trivial or repetitive
        actions against your will [syn: {obsession}]
     3: using force to cause something; "though pressed into rugby
        under compulsion I began to enjoy the game"; "they didn`t
        have to use coercion" [syn: {coercion}]