Merriam-Webster's Collegiate® Dictionary, 11th Edition
VOLUNTEER
I. noun
Etymology: obsolete French voluntaire (now volontaire), from voluntaire, adjective , voluntary, from Old French, from Latin voluntarius
Date: circa 1600
a person who voluntarily undertakes or expresses a willingness to undertake a service: as, one who enters into military service voluntarily, b. one who renders a service or takes part in a transaction while having no legal concern or interest, one who receives a conveyance or transfer of property without giving valuable consideration, a volunteer plant, a member of a quasi-military religious and philanthropic organization founded in 1896 by Commander and Mrs. Ballington Booth,
II. adjective
Date: 1649
being, consisting of, or engaged in by volunteers , growing spontaneously without direct human control or supervision especially from seeds lost from a previous crop ,
III. verb
Date: circa 1755
intransitive verb to offer oneself as a volunteer , transitive verb to offer or bestow voluntarily