Definition of "campaigner"

campaigner

/kæmˈpeɪnə(ɹ)/

noun
plural campaigners
1. A person who has served in a military campaign.
2. (by extension) A military veteran.
3. A person who campaigns for a person running for political office or works, or supports, in an organised and active way towards a goal; an activist.
  Quotations
  The US supreme court has ruled unanimously that natural human genes cannot be patented, a decision that scientists and civil rights campaigners said removed a major barrier to patient care and medical innovation.
  2013 June 21, Karen McVeigh, “US rules human genes can't be patented”, in The Guardian Weekly, volume 189, number 2, page 10
  It is remembered unfondly by politicians, communities and campaigners as the document that heralded widespread reductions in the size of the railway.
  2023 March 8, Gareth Dennis, “The Reshaping of things to come...”, in RAIL, number 978, page 44
4. Someone with experience in a certain field.