campaigner - definition and synonyms

noun [countable] 

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/ˌkæmˈpeɪnə(r)/
  1. someone who tries to achieve political or social change by persuading other people or the government to do something

    Animal rights campaigners are trying to close down the farm.

    campaigner for/against:

    Campaigners against the new road have marched through the streets waving banners.