The Collaborative International Dictionary of English v.0.48:

Free will \Free will\
   1. A will free from improper coercion or restraint.
      [1913 Webster]

            To come thus was I not constrained, but did
            On my free will.                      --Shak.
      [1913 Webster]

   2. The power asserted of moral beings of willing or choosing
      without the restraints of physical or absolute necessity.
      [1913 Webster] free-will

WordNet (r) 3.0 (2006):

free will
    n 1: the power of making free choices unconstrained by external
         agencies [syn: free will, discretion]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "free will":
   alternativity, animus, appetence, appetency, appetite,
   autonomousness, autonomy, choice, choosing, co-optation, co-option,
   command, conation, conatus, decision, desire, determination,
   discretion, disposition, election, fancy, first choice,
   free choice, free decision, full consent, gratuitousness,
   inclination, independence, intention, liking, lust, mind,
   noncontingent free will, objective, option, passion, pick,
   pleasure, preference, preoption, resolution, say, say-so,
   selection, self-action, self-activity, self-determination,
   sexual desire, spontaneity, spontaneousness, the pick,
   unforcedness, velleity, volition, voluntariness, voluntarism,
   voluntaryism, volunteer, volunteering, will, will power, wish