perfidious

Of, relating to, or marked by perfidy; treacherous. synonym: faithless.

Faithless; basely treacherous; false-hearted.

Proceeding from or characterized by perfidy or base treachery; false: as, a perfidious act.

Guilty of perfidy; violating good faith or vows; false to trust or confidence reposed; teacherous; faithless.

Involving, or characterized by, perfidy.

Of, pertaining to, or representing perfidy; disloyal to what should command one’s fidelity or allegiance.

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