Synonyms for Duplicitous (same or very similar meaning)
WordNet sense 1 (marked by deliberate deceptiveness especially by pretending one set of feelings and acting under the influence of another):
ambidextrous, deceitful, double-dealing, two-faced, double-faced, double-tongued, Janus-facedWordNet sense 2 (deceptive or fraudulent; disposed to cheat or defraud or deceive):
dishonest, dishonorableFrom the ODE community, based on WordNetadd/edit