voluntary -
composition (often improvised) for a solo instrument (especially solo organ) and not a regular part of a religious service or musical performance
solo a flight in which the aircraft pilot is unaccompanied
voluntary -
(military) a person who freely enlists for service
voluntary -
of your own free will or design; done by choice; 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"
nonvoluntary,
unvoluntary,
involuntary not subject to the control of the will; "involuntary manslaughter"; "involuntary servitude"; "an involuntary shudder"; "It (becoming a hero) was involuntary. They sank my boat"- John F.Kennedy
conscious (followed by `of') showing realization or recognition of something; "few voters seem conscious of the issue's importance"; "conscious of having succeeded"; "the careful tread of one conscious of his alcoholic load"- Thomas Hardy
willing disposed or inclined toward; "a willing participant"; "willing helpers"