Duplicity, n.; pl. Duplicities.
Etymology: [F. duplicité, L. duplicitas, fr. duplex double. See Duplex.]
1. Doubleness; a twofold state. [Archaic] Do not affect duplicities nor triplicities, nor any certain number of parts in your division of things. I. Watts.
2. Doubleness of heart or speech; insincerity; a sustained form of deception which consists in entertaining or pretending to entertain one of feelings, and acting as if influenced by another; bad faith. Far from the duplicity wickedly charged on him, he acted his part with alacrity and resolution. Burke.
3. (Law) (a) The use of two or more distinct allegations or answers, where one is sufficient. Blackstone. (b) In indictments, the union of two incompatible offenses. Wharton.
Syn. -- Double dealing; dissimulation; deceit; guile; deception; falsehood.
Shades of meaning
Fernald has no entry of its own for duplicity; he lists it under deception, fraud.
Where he writes about it:
Duplicity is the habitual speaking or acting with intent to appear to mean what one does not. — from deception