Definition of Judas Jew in US English:

Judas Jew

noun

rare, offensive
  • A person whose treachery resembles that of Judas; (in later use more usually) a Jew likened to Judas in having committed an act of betrayal, disloyalty, etc.

Origin

Mid 17th century; earliest use found in George Herbert (1593–1633), Church of England clergyman and poet.