voluntary

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Done or undertaken of one's own free will.
• adjective Acting or done willingly and without constraint or expectation of reward.
• adjective Normally controlled by or subject to individual volition.
• adjective Capable of making choices; having the faculty of will.
• adjective Supported by contributions or charitable donations rather than by government appropriations.
• adjective Without legal obligation or consideration.
• adjective Done intentionally but without premeditation or deliberation, as when under the influence of an intense emotional reaction.
• noun A short piece of music, often improvised on a solo instrument, played as an introduction to a larger work.
• noun A piece for solo organ, often improvised, played before, during, or after a religious service.
• noun A volunteer.

from The Century Dictionary.

• Voluntarily.
• Proceeding from the will: done of or due to one's own accord or free choice; unconstrained by external interference, force, or influence; not compelled, prompted, or suggested by another; spontaneous; of one's or its own accord; free.
• Subject to or controlled by the will; regulated by the will: as, the movement, of a limb is voluntary, the action of the heart involuntary.
• Done by design or intention; intentional; purposed; not accidental.
• Endowed with the power of willing, or acting of one's own free will or choice, or according to one's judgment.
• Of, pertaining, or relating to voluntaryism, or the doctrines of the voluntaries: as, the voluntary theory or controversy.
• In law: Proceeding from the free and unconstrained will of the person: as, a voluntary confession.
• Not supported by a substantial pecuniary or valuable consideration. See voluntary conveyance, below
• An affidavit offered spontaneously or made freely, without the compulsion of subpoena or other process.
• noun One who engages in any affair of his own choice or free will; a volunteer.
• noun Specifically Eccles., in Great. Britain, one who maintains the doctrine of the mutual independence of the church and the state, and holds that the church should be supported by the voluntary contributions of its members and should be left entirely free to regulate its affairs.
• noun Any work or performance not imposed by another.
• noun In church music, an organ prelude to a service; sometimes, by extension, an interlude or postlude; also, an anthem or other piece of choir-music, especially at the opening of a service.

from the GNU version of the Collaborative International Dictionary of English.

• noun rare One who engages in any affair of his own free will; a volunteer.
• noun (Mus.) A piece played by a musician, often extemporarily, according to his fancy; specifically, an organ solo played before, during, or after divine service.
• noun (Eccl.) One who advocates voluntaryism.
• adjective Proceeding from the will; produced in or by an act of choice.
• adjective 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.
• adjective Done by design or intention; intentional; purposed; intended; not accidental.
• adjective (Physiol.) Of or pertaining to the will; subject to, or regulated by, the will.
• adjective Endowed with the power of willing.
• adjective (Law) Free; without compulsion; according to the will, consent, or agreement, of a party; without consideration; gratuitous; without valuable consideration.
• adjective (Eccl.) Of or pertaining to voluntaryism.
• adjective (Law) an affidavit or oath made in an extrajudicial matter.
• adjective (Law) a conveyance without valuable consideration.
• adjective (Law) the escape of a prisoner by the express consent of the sheriff.
• adjective (Eng. Eccl. Law) See Contentious jurisdiction, under Contentious.
• adjective (Law) See Waste, n., 4.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Done, given, or acting of one's own free will.
• adjective Working or done without payment.
• adverb obsolete Voluntarily.
• noun music A short piece of music, often having improvisation, played on a solo instrument
• noun A volunteer

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective of your own free will or design; done by choice; not forced or compelled
• noun (military) a person who freely enlists for service
• noun composition (often improvised) for a solo instrument (especially solo organ) and not a regular part of a religious service or musical performance
• adjective controlled by individual volition