What does "perfidious" mean?

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

What is a synonym for "perfidious"?

Common synonyms include: treacherous, alienated, ambidextrous, artful, bad intention, black.

/pɚˈfɪdi.əs/ adj

adj ·Uncommon ·College level

Adjective

1
Of, pertaining to, or representing perfidy; disloyal to what should command one's fidelity or allegiance.
"TRINCULO (speaking about Caliban): By this light, a most perfidious and drunken / monster: when his god's asleep, he'll rob his bottle."

Adjective

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

"The most perfidious way of harming a cause consists of defending it deliberately with faulty arguments."

From Latin perfidiōsus (“treacherous”), from perfidia.