The Collaborative International Dictionary of English v.0.48:

Hankey-pankey \Han"key-pan"key\, Hankey-pank
\Han"key-pank`\(h[a^][ng]"k[y^]*p[a^][ng]"k[y^]), n. [Cf.
   Hocus-pocus.] [Also spelled hanky-panky.]
   1. Professional cant; the chatter of conjurers to divert
      attention from their tricks; hence, jugglery. [Colloq.]
      [1913 Webster]

   2. Illegal or unethical behavior, usually surreptitious; as,
      the boss got suspicious when profits seemed lower than
      expected, and hired an investigator to see if any
      hankey-pankey was going on. [Informal]
      [PJC]

   3. Extramarital sexual relations, especially adultery.
      [Colloq.]
      [PJC]