[1] : The Collaborative International Dictionary of English v.0.48

campaigner \campaign"er\, n.
   1. one who has served in an army in several campaigns; an old
      soldier; a veteran.
      1913 webster

   2. one who is campaigning, especially a politician running
      for elective office, or one of his/her supporters.
      pjc

[2] : WordNet (r) 2.0

campaigner
     n : a politician who is running for public office syn: candidate,
          nominee
see also:
candidate nominee 

Campaigner >> C Words
Campaigner, definition of term: Campaigner
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