backstabber
/ˈbækˌstæbər/
noun
- A person who betrays someone they pretend to be friends with, especially by saying or doing something harmful behind that person's back.
- The team was full of backstabbers who would do anything to get ahead, even if it meant hurting their coworkers.
- I thought she was my best friend, but she turned out to be a backstabber who spread rumors about me.
- He learned the hard way not to trust a backstabber when his business partner secretly sold their company out from under him.