Definition of "volunteer"

volunteer

/ˌvɒl(ə)nˈtɪə/

noun
plural volunteers
1. One who enters into, or offers themselves for, any service of their own free will, especially when done without pay.
2. (military) One who enters into military service voluntarily (but who, when in service, is subject to discipline and regulations like other soldiers), as opposed to a conscript.
3. (military) A voluntary member of the organized militia of a country, as distinguished from a regular or member of the standing army.
  Quotations
  That summer and fall the Army organized twenty-five regiments of volunteers, including two black regiments, which would have all-black captains and lieutenants. All officers were to be selected from regulars and volunteers who had distinguished themselves […]
  2007 April 30, Edward M. Coffman, The Regulars: The American Army, 1898-1941, Harvard University Press, page 16
4. (law) A person who acts out of their own will without a legal obligation, such as a donor.
5. (botany, agriculture) A plant that grows spontaneously, without being cultivated on purpose; see volunteer plant in Wikipedia.
6. A native or resident of the American state of Tennessee.
verb
third-person singular simple present volunteers, present participle volunteering, simple past and past participle volunteered
1. (intransitive) To enlist oneself as a volunteer.
2. (transitive, intransitive) To do or offer to do something voluntarily.
  Quotations
  Miranda: No good. Both routes are blocked. See these doors? The only way past is to get someone to open them from the other side.Shepard: It's not a fortress; there's got to be something. Here, maybe we can send someone in through this ventilation shaft.Jacob: Practically a suicide mission. I volunteer.Miranda: I appreciate the thought, Jacob, but you couldn't shut down the security systems in time. We need to send a tech expert.
  2010, BioWare, Mass Effect 2 (Science Fiction), Redwood City: Electronic Arts, PC, scene: Normandy SR-2
3. (transitive) To offer, usually unprompted.
4. (transitive, informal) To offer the services of (someone else) to do something.
5. (intransitive, botany) To grow without human sowing or intentional cultivation.