1. 背信弃义的；不可信的；不忠的
If you describe someone as perfidious, you mean that they have betrayed someone or cannot be trusted.

1. tending to betray
especially having a treacherous character as attributed to the Carthaginians by the Romans

e.g. Punic faith
the perfidious Judas
the fiercest and most treacherous of foes
treacherous intrigues

Synonym: punictreacherous