Definition from Wiktionary, the free dictionary
volunteer (plural volunteers)
- One who enters into, or offers for, any service of his/her own free will, especially when done without pay.
- (military) 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.
- (law) A person who acts out of his own will without a legal obligation, such as a donor.
- (botany, agriculture) 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.
Related terms 
one who voluntarily offers himself/herself for service
one who acts without legal obligation
- The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.
Translations to be checked
- (intransitive) To enlist oneself as a volunteer.
- (transitive, intransitive) To do or offer to do something voluntarily.
- to volunteer for doing the dishes
- to volunteer an explanation
- (intransitive, botany) To grow without human sowing or intentional cultivation.
to enlist oneself as a volunteer
to do or offer to do something voluntarily