"voluntary" in the noun sense
1. volunteer, military volunteer, voluntary
military) a person who freely enlists for service
composition (often improvised) for a solo instrument (especially solo organ) and not a regular part of a religious service or musical performance
"voluntary" in the adjective sense
of your own free will or design done by choice not forced or compelled
"man is a voluntary agent"
"participation was voluntary"
"voluntary generosity in times of disaster"
"voluntary social workers"
"a voluntary confession"
controlled by individual volition
Source: WordNet® (An amazing lexical database of English)
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