" double-crosser "

1: one who betrays a trust or an allegiance;

  * e.g., " ... we knew he was a double-crosser so we didn't tell him our real plans "

•  Synonyms : 

•  apostate,

•  backstabber,

•  betrayer,

•  double-dealer,

•  Judas,

•  quisling,

•  recreant,

•  serpent,

•  snake,

•  traitor,

•  turncoat

•  Antonyms : 

• (N/A)

1: to be unfaithful or disloyal to;

  * e.g., " ... she promised to share the profits but then double-crossed us "

•  Synonyms : 

•  backstab,

•  betray,

•  cross,

•  sell (out),

•  two-time

•  Antonyms : 

•  stand by