vol·un·tar·y / ˈvälənˌterē/ • adj. done, given, or acting of one's own free will: we are funded by voluntary contributions. ∎  working, done, or maintained without payment: a voluntary helper. ∎  supported by contributions rather than taxes or fees: voluntary hospitals. ∎  Physiol. under the conscious control of the brain. ∎ Law (of a conveyance or disposition) made without return in money or other consideration.• n. (pl. -tar·ies) an organ solo played before, during, or after a church service. ∎ hist. a piece of music performed extempore, esp. as a prelude to other music, or composed in a free style. DERIVATIVES: vol·un·tar·i·ly / ˌvälənˈte(ə)rəlē; ˈvälənˌter-/ adv.vol·un·tar·i·ness n.

voluntary adj. XIV; sb. piece of music selected by an organist to be played e.g. while a congregation departs XVIII. — (partly after (O)F. volontaire, †voluntaire) L. voluntārius, f. voluntās will, for *voluntitās, f. prp. form of the same type as eunt- going (f. volō I WILL2) + tās -TY2; see -ARY.
So volunteer one who voluntarily offers his services, orig. mil. XVII. — F. volontaire — L. voluntārius; the suffix was assim. to -IER2 and (later) -EER. Hence volunteering XVII; whence by back-formation volunteer vb. XVIII.

voluntary.
1. Org. solo at beginning and end of Anglican church service, sometimes but not necessarily extemporized.

2.   In 16th cent., applied to extemporized instr. comp. See also trumpet tune or voluntary.

voluntary Controlled by conscious thought. See voluntary muscle. Compare involuntary.