Dictionary.net

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"

dangerously unstable and unpredictable; "treacherous winding roads"; "an unreliable trestle"

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"

dangerously unstable and unpredictable; "treacherous winding roads"; "an unreliable trestle"

Betraying a trust or a pledge; apparently good, strong, honest, etc., but in reality the opposite; as, a treacherous smile; treacherous ice, etc.; faithless.

Treacherously.

Treacherousness.

Treacherously.

Treacherousness.

Full of treachery: faithless.

Faithless; perfidious.

Traitorous; false.