voluntary vs willing

voluntary and willing both are nouns.

Word	Noun	Adjective	Verb	Adverb
voluntary	Yes	Yes	No	No
willing	Yes	Yes	No	No

voluntary (noun)	willing (noun)
composition (often improvised) for a solo instrument (especially solo organ) and not a regular part of a religious service or musical performance	the act of making a choice
(military) a person who freely enlists for service

voluntary (adjective)	willing (adjective)
of your own free will or design; done by choice; not forced or compelled	disposed or inclined toward
controlled by individual volition	not brought about by coercion or force