Definition of: perfidious

(pər·fid′ē·əs) adjective
1. Characterized by or guilty of perfidy; treacherous.
2. Involving a breach of faith; contrary to loyalty and truth. [<L perfidiosus <perfidia PERFIDY]
—per·fid′i·ous·ly adverb
—per·fid′i·ous·ness noun Synonyms: deceitful, disloyal, double–faced, faithless, false, forsworn, perjured, traitorous, treacherous, two–faced, unfaithful, untrue, untrustworthy. Antonyms: faithful, honest, incorruptible, staunch, steadfast, true, trustworthy, trusty.