The Collaborative International Dictionary of English v.0.48:

duplicity \du*plic"i*ty\, n.; pl. duplicities. [F.
   duplicit['e], L. duplicitas, fr. duplex double. See
   Duplex.]
   1. Doubleness; a twofold state. [Archaic]
      [1913 Webster]

            Do not affect duplicities nor triplicities, nor any
            certain number of parts in your division of things.
                                                  --I. Watts.
      [1913 Webster]

   2. 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.
      [1913 Webster]

            Far from the duplicity wickedly charged on him, he
            acted his part with alacrity and resolution.
                                                  --Burke.
      [1913 Webster]

   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.
        [1913 Webster]

WordNet (r) 3.0 (2006):

duplicity
    n 1: a fraudulent or duplicitous representation [syn:
         fraudulence, duplicity]
    2: acting in bad faith; deception by pretending to entertain one
       set of intentions while acting under the influence of another
       [syn: duplicity, double-dealing]