The Collaborative International Dictionary of English v.0.48:

Amour \A*mour"\, n. [F., fr. L. amor love.]
   1. Love; affection. [Obs.]
      [1913 Webster]

   2. Love making; a love affair; usually, an unlawful
      connection in love; a love intrigue; an illicit love
      affair.
      [1913 Webster]

   In amours with, in love with. [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

amour
    n 1: a usually secretive or illicit sexual relationship [syn:
         affair, affaire, intimacy, liaison, involvement,
         amour]