Perfidious, a.
Etymology: [L. perfidious.]
1. Guilty of perfidy; violating good faith or vows; false to trust or confidence reposed; teacherous; faithless; as, a perfidious friend. Shak.
2. Involving, or characterized by, perfidy. "Involved in this perfidious fraud." Milton.
Shades of meaning
Fernald lists perfidious only as an antonym, under honest.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given