intervenor

/ˌɪntərˈvinər/
noun
  1. A person or group that becomes involved in a situation, especially a legal case or dispute, to influence the outcome.
    • The judge allowed the community organization to join as an intervenor.
    • As an intervenor, she presented evidence to support the workers' rights.
    • The environmental group became an intervenor in the court case about the new factory.
Antonyms
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