cuckoldry

from WordNet (r) 3.0 (2006)

cuckoldry
    n 1: the practice of making cuckolds; sexual conquests of
         married women

from The Collaborative International Dictionary of English v.0.48

Cuckoldry \Cuck"old*ry\ (-?ld-r?), n.
   The state of being a cuckold; the practice of making
   cuckolds.
   [1913 Webster]

from Moby Thesaurus II by Grady Ward, 1.0

28 Moby Thesaurus words for "cuckoldry":
      adulterous affair, adultery, affair, amour, concubinage,
      criminal conversation, entanglement, eternal triangle,
      extracurricular sex, extramarital relations, flirtation,
      forbidden love, fornication, free love, free-lovism, hanky-panky,
      illicit love, incest, infidelity, intrigue, liaison, love affair,
      premarital relations, premarital sex, romance, romantic tie,
      triangle, unfaithfulness