voluntary

Concise Oxford English Dictionary © 2008 Oxford University Press:
voluntary/ˈvɒləntri/

▶adjective

• 1 done, given, or acting of one's own free will.

  ■ Physiology under the conscious control of the brain.

• 2 working or done without payment.

  ■ Law (of a conveyance or disposition) made without return in money or other consideration.

▶noun (pl. voluntaries)

• 1 an organ solo played before, during, or after a church service.

  ■ historical a piece of music performed extempore or composed in a free style.

• 2 (in a competition) a special performance left to the performer's choice.

– derivatives
voluntarily adverb,
voluntariness noun.

– origin ME: from OFr. volontaire or L. voluntarius, from voluntas ‘will’.