°One who enters into, or offers for, any
service of his/her own free will, especially when done without pay.
°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.
verb
°To enlist oneself as a volunteer.
°To do or offer to do something voluntarily.