volunteer

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 volunteer for doing the dishes”

To offer, usually unprompted.

“to volunteer an explanation”

To grow without human sowing or intentional cultivation.

To offer the services of (someone else) to do something.

“My sister volunteered me to do the dishes.”