The Collaborative International Dictionary of English v.0.48:

Appetency \Ap"pe*ten*cy\, n.; pl. Appetencies. [L. appetentia,
   fr. appetere to strive after, long for. See Appetite.]
   1. Fixed and strong desire; esp. natural desire; a craving;
      an eager appetite.
      [1913 Webster]

            They had a strong appetency for reading. --Merivale.
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   2. Specifically: An instinctive inclination or propensity in
      animals to perform certain actions, as in the young to
      suck, in aquatic fowls to enter into water and to swim;
      the tendency of an organized body to seek what satisfies
      the wants of its organism.
      [1913 Webster]

            These lacteals have mouths, and by animal selection
            or appetency the absorb such part of the fluid as is
            agreeable to their palate.            --E. Darwin.
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   3. Natural tendency; affinity; attraction; -- used of
      inanimate objects.
      [1913 Webster]

WordNet (r) 3.0 (2006):

appetency
    n 1: a feeling of craving something; "an appetite for life";
         "the object of life is to satisfy as many appetencies as
         possible"- Granville Hicks [syn: appetite, appetency,
         appetence]