traitor

/ˈtreɪtər/
noun
  1. A person who betrays their country, group, or friends by helping an enemy or acting against them.
    • She felt like a traitor when she moved to a rival company and took her old team's clients.
    • The soldier was labeled a traitor after giving secret information to the enemy.
    • In the story, the king's closest advisor turned out to be a traitor who planned a rebellion.
  2. A person who betrays a trust, principle, or cause.
    • Some fans considered the player a traitor for leaving the team to join their biggest rival.
    • Environmentalists called him a traitor to the cause when he accepted money from a polluting factory.
    • He was seen as a traitor to his own values when he lied to protect his reputation.