tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans; "Punic faith"; "the perfidious Judas"; "the fiercest and most treacherous of foes"; "treacherous intrigues"
Guilty of perfidy; violating good faith or vows; false to trust or confidence reposed; teacherous; faithless; as, a perfidious friend
If you describe someone as perfidious, you mean that they have betrayed someone or cannot be trusted. Their feet will trample on the dead bodies of their perfidious aggressors. = treacherous. someone who is perfidious is not loyal and cannot be trusted = treacherous (perfidiosus, from perfidia , from perfidus , from per fidem decipere )
Of, pertaining to, or representing perfidy; disloyal to what should command ones fidelity or allegiance