One who enters into, or offers for, any service of his/her own free will, especially when done without pay.
One who enters into military service voluntarily, but who, when in service, is subject to discipline and regulations like other soldiers; -- opposed to conscript; specifically, a voluntary member of the organized militia of a country as distinguished from the standing army.
A person who acts out of his own will without a legal obligation, such as a donor.
A plant that grows spontaneously, without being cultivated on purpose; see volunteer plant in Wikipedia.
A native or resident of the American state of Tennessee.
To enlist oneself as a volunteer.
To do or offer to do something voluntarily.
To offer, usually unprompted.
To grow without human sowing or intentional cultivation.
To offer the services of (someone else) to do something.