dissident
  (a.)意見不同的,不同意的,不贊成的意見不同的人,不贊成者

 ”This is a crucial moment. Cuba wants change, the people want change,” said Oswaldo Paya, Cuba’s best-known dissident.  Fidel Castro steps down after 49-year rule, 20.02.2008,  http://www.reuters.com/article/topNews/idUSN1941945720080219?feedType=RSS&feedName=topNews&pageNumber=2&virtualBrandChannel=0.