volunteer

Concise Oxford English Dictionary © 2008 Oxford University Press:
volunteer/vɒlənˈtɪə(r)/

▶noun

• 1 a person who freely offers to do something.

  ■ a person who freely enrols for military service rather than being conscripted.

• 2 a person who works for an organization without being paid.

• 3 a plant that has not been deliberately planted.

• 4 Law a person to whom a voluntary conveyance or disposition is made.

▶verb

• 1 freely offer to do something.

  ■ commit (someone) to an undertaking without consulting them.

• 2 say or suggest something without being asked.

• 3 work for an organization without being paid.

– origin C16 (as n.): from Fr. volontaire ‘voluntary’.