Doubleness of heart or speech; insincerity; a sustained form of deception which consists in entertaining or pretending to entertain one set of feelings, and acting as if influenced by another; bad faith
If you accuse someone of duplicity, you mean that they are deceitful. Malcolm believed he was guilty of duplicity in his private dealings. = deceit. dishonest behaviour that is intended to deceive someone (duplicité, from duplex; DUPLEX)
acting in bad faith; deception by pretending to entertain one set of intentions while acting under the influence of another