The Collaborative International Dictionary of English v.0.48:

Voluntary \Vol"un*ta*ry\, a. [L. voluntarius, fr. voluntas will,
   choice, from the root of velle to will, p. pr. volens; akin
   to E. will: cf. F. volontaire, Of. also voluntaire. See
   Will, v. t., and cf. Benevolent, Volition,
   Volunteer.]
   1. Proceeding from the will; produced in or by an act of
      choice.
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            That sin or guilt pertains exclusively to voluntary
            action is the true principle of orthodoxy. --N. W.
                                                  Taylor.
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   2. Unconstrained by the interference of another; unimpelled
      by the influence of another; not prompted or persuaded by
      another; done of his or its own accord; spontaneous;
      acting of one's self, or of itself; free.
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            Our voluntary service he requires.    --Milton.
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            She fell to lust a voluntary prey.    --Pope.
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   3. Done by design or intention; intentional; purposed;
      intended; not accidental; as, if a man kills another by
      lopping a tree, it is not voluntary manslaughter.
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   4. (Physiol.) Of or pertaining to the will; subject to, or
      regulated by, the will; as, the voluntary motions of an
      animal, such as the movements of the leg or arm (in
      distinction from involuntary motions, such as the
      movements of the heart); the voluntary muscle fibers,
      which are the agents in voluntary motion.
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   5. Endowed with the power of willing; as, man is a voluntary
      agent.
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            God did not work as a necessary, but a voluntary,
            agent, intending beforehand, and decreeing with
            himself, that which did outwardly proceed from him.
                                                  --Hooker.
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   6. (Law) Free; without compulsion; according to the will,
      consent, or agreement, of a party; without consideration;
      gratuitous; without valuable consideration.
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   7. (Eccl.) Of or pertaining to voluntaryism; as, a voluntary
      church, in distinction from an established or state
      church.
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   Voluntary affidavit or Voluntary oath (Law), an affidavit
      or oath made in an extrajudicial matter.

   Voluntary conveyance (Law), a conveyance without valuable
      consideration.

   Voluntary escape (Law), the escape of a prisoner by the
      express consent of the sheriff.

   Voluntary jurisdiction. (Eng. Eccl. Law) See Contentious
      jurisdiction, under Contentious.

   Voluntary waste. (Law) See Waste, n., 4.
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   Syn: See Spontaneous.
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Bouvier's Law Dictionary, Revised 6th Ed (1856):

VOLUNTARY JURISDICTION. In the ecclesiastical law, jurisdiction is either
contentious jurisdiction, (q.v.) or voluntary jurisdiction. By the latter
term is understood that kind of jurisdiction which requires no judicial
proceedings, as, the granting letters of administration and receiving the
probate of wills.