campaigner

Concise Oxford English Dictionary © 2008 Oxford University Press:
campaign/kamˈpeɪn/

▶noun

• 1 a series of military operations intended to achieve an objective in a particular area.

• 2 an organized course of action to achieve a goal.

▶verb work in an organized and active way towards a goal.

– derivatives
campaigner noun.

– origin C17 (denoting a tract of open country): from Fr. campagne, via Ital. from late L. campania, from campus (see camp1).