Source : Webster's Revised Unabridged Dictionary (1913)

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.

            That sin or guilt pertains exclusively to voluntary
            action is the true principle of orthodoxy. --N. W.
                                                  Taylor.

   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.

            Our voluntary service he requires.    --Milton.

            She fell to lust a voluntary prey.    --Pope.

   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.

   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.

   5. Endowed with the power of willing; as, man is a voluntary
      agent.

            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.

   6. (Law) Free; without compulsion; according to the will,
      consent, or agreement, of a party; without consideration;
      gratuitous; without valuable consideration.

   7. (Eccl.) Of or pertaining to voluntaryism; as, a voluntary
      church, in distinction from an established or state
      church.

   {Voluntary affidavit} or {oath} (Law), an affidavit or oath
      made in 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.

   Syn: See {Spontaneous}.

Voluntary \Vol"un*ta*ry\, n.; pl. {Voluntaries}.
   1. One who engages in any affair of his own free will; a
      volunteer. [R.] --Shak.

   2. (Mus.) A piece played by a musician, often extemporarily,
      according to his fancy; specifically, an organ solo played
      before, during, or after divine service.

   3. (Eccl.) One who advocates voluntaryism.

Source : WordNet®

voluntary
     adj 1: of your own free will or design; not forced or compelled;
            "man is a voluntary agent"; "participation was
            voluntary"; "voluntary manslaughter"; "voluntary
            generosity in times of disaster"; "voluntary social
            workers"; "a voluntary confession" [ant: {involuntary}]
     2: controlled by individual volition; "voluntary motions";
        "voluntary muscles" [ant: {involuntary}]

voluntary
     n 1: (military) a person who freely enlists for service [syn: {volunteer},
           {military volunteer}] [ant: {draftee}]
     2: composition (often improvised) for a solo instrument
        (especially solo organ) and not a regular part of a
        service or performance