Perfidious
Perfidious (pẽr*fid"i*us; 277) , adjective
[Latin perfidious.]
1.
Guilty of perfidy; violating good faith or vows; false to trust or confidence reposed; treacherous; faithless; as, a perfidious friend. — Shakespeare
2.
Involving, or characterized by, perfidy.
Involved in this perfidious fraud.