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 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.
• 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 In horticulture, a plant that comes up of itself from naturally scattered seed, in distinction from one that comes from sowing by the horticulturist.

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

• intransitive verb To enter into, or offer for, any service of one's own free will, without solicitation or compulsion.
• 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.
• adjective Of or pertaining to a volunteer or volunteers; consisting of volunteers; voluntary
• transitive verb To offer or bestow voluntarily, or 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