perfidious

Modifies a noun

• role: It is precisely on this question that the perfidious role of the Popular Front was very strikingly revealed.
• act: It may be possible through imitative deception to commit perfidious acts.
• nature: Indeed, they are taken as a sign of his integrity and the perfidious nature of his detractors.
• friend: In my own Foreign Office experience, moral language as such was rarely used about policy, only about enemies and perfidious friends.