turn traitor

English

Verb

turn traitor (third-person singular simple present turns traitor, present participle turning traitor, simple past and past participle turned traitor)

1. To become a traitor, by betraying a person, group, or one's country.
   • 1980, AA Book of British Villages, Drive Publications Ltd, page 134, about Corfe Castle:

     For a time, it was the only Royalist stronghold between London and Exeter, but it fell at last when a member of the garrison turned traitor and admitted the Parliamentary besiegers who destroyed it with gunpowder.

References

• “turn traitor”, in Merriam-Webster Online Dictionary, Springfield, Mass.: Merriam-Webster, 1996–present.
• Oxford Dictionary of English.