WordNet (r) 3.0 (2006):

hanky panky
    n 1: verbal misrepresentation intended to take advantage of you
         in some way [syn: trickery, hocus-pocus, slickness,
         hanky panky, jiggery-pokery, skulduggery,
         skullduggery]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "hanky panky":
   adulterous affair, adultery, affair, amour, conjuration, cuckoldry,
   entanglement, escamotage, eternal triangle, flirtation,
   forbidden love, hocus-pocus, hokey-pokey, illicit love, infidelity,
   intrigue, jiggery-pokery, jugglery, juggling, legerdemain, liaison,
   love affair, monkey business, mumbo jumbo, prestidigitation,
   romance, romantic tie, sleight of hand, triangle, trickery,
   unfaithfulness