n. In horticulture, a plant that comes up of itself from naturally scattered seed, in distinction from one that comes from sowing by the horticulturist.n. A person who enters into any service of his own free will.n. 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.n. 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.n. 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