Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

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