The Collaborative International Dictionary of English v.0.48:

Preoccupancy \Pre*oc"cu*pan*cy\, n. [See Preoccupate.]
   The act or right of taking possession before another; as, the
   preoccupancy of wild land.
   [1913 Webster]

WordNet (r) 3.0 (2006):

preoccupancy
    n 1: the mental state of being preoccupied by something [syn:
         preoccupation, preoccupancy, absorption,
         engrossment]
    2: the act of taking occupancy before someone else does [syn:
       preoccupancy, preoccupation]