volunteer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A person who performs or offers to perform a service voluntarily.
• noun A person who chooses to enter a branch of the military without being drafted or forced to do so by law.
• noun Law A person who works without pay or assumes an obligation to which he or she is not a party or otherwise interested.
• noun Botany A cultivated plant growing from self-sown or accidentally dropped seed.
• adjective Being, consisting of, or done by volunteers.
• adjective Botany Growing from self-sown or accidentally dropped seed. Used of a cultivated plant or crop.
• intransitive verb To give or offer to give voluntarily.
• intransitive verb Informal To compel (someone) to do something.
• intransitive verb To perform or offer to perform a service of one's own free will.
• intransitive verb To choose to enter military service of one's own free will.
• intransitive verb To do charitable or helpful work without pay.

from The Century Dictionary.

• noun In horticulture, a plant that comes up of itself from naturally scattered seed, in distinction from one that comes from sowing by the horticulturist.
• To offer, contribute, or bestow voluntarily, or without constraint or compulsion.
• To enter into any service of one's free will, without constraint or compulsion: as, to volunteer for a campaign
• noun A person who enters into any service of his own free will.
• noun A person who enters military service of his own free will, and not by constraint or compulsion; one who offers to serve, and generally receives some consideration or privileges on that account; in the United States, especially during the civil war, a soldier of a body other than the regular army, but practically governed by the same laws when in service.
• noun In law, one who claims the benefit of a contract or conveyance although no consideration proceeded from him nor from any one in whose place he stands.
• noun A tree which grows spontaneously: as, that pear-tree in my garden is a volunteer.
• Entering into military service by free will and choice: as, a volunteer soldier.
• Composed of volunteers: as, a volunteer corps.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of or pertaining to a volunteer or volunteers; consisting of volunteers; voluntary
• noun One who enters into, or offers for, any service of his own free will.
• noun (Mil.) One who enters into 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.
• noun (Law) A grantee in a voluntary conveyance; one to whom a conveyance is made without valuable consideration; a party, other than a wife or child of the grantor, to whom, or for whose benefit, a voluntary conveyance is made.
• transitive verb To offer or bestow voluntarily, or without solicitation or compulsion.
• intransitive verb To enter into, or offer for, any service of one's own free will, without solicitation or compulsion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One who enters into, or offers for, any service of his/her own free will, especially when done without pay.
• noun 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.
• noun law A person who acts out of his own will without a legal obligation, such as a donor.
• noun botany A plant that grows in disturbed soil.
• noun A native or resident of the American state of Tennessee.
• verb intransitive To enlist oneself as a volunteer.
• verb transitive To do or offer to do something voluntarily.
• verb intransitive, botany To grow without human sowing or intentional cultivation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a person who performs voluntary work
• adjective without payment
• verb tell voluntarily
• noun (military) a person who freely enlists for service
• verb agree freely
• verb do volunteer work
• noun a native or resident of Tennessee