double crosser
/ˈdʌbəl ˈkrɔsər/
noun
- A person who deceives or betrays someone they were supposed to be loyal to, especially after pretending to be an ally.
- No one trusted him after he proved to be a double-crosser in the business deal.
- In the movie, the hero's best friend turned out to be a double-crosser.
- The spy was revealed to be a double-crosser working for the enemy.
Antonyms