The Collaborative International Dictionary of English v.0.48:

Occupancy \Oc"cu*pan*cy\, n. [See Occupant.]
   1. The act of taking or holding possession, especially of
      real property or rental property; possession; occupation.
      [1913 Webster]

   2. The state or condition of being occupied; as, occupancy by
      more than 250 people is dangerous and unlawful.
      [PJC]

   3. The period of time during which one occupies a property.
      [PJC]

   Title by occupancy (Law), a right of property acquired by
      taking the first possession of a thing, or possession of a
      thing which belonged to nobody, and appropriating it.
      --Blackstone. Kent.
      [1913 Webster]

WordNet (r) 3.0 (2006):

occupancy
    n 1: an act of being a tenant or occupant [syn: occupancy,
         tenancy]
    2: the act of occupying or taking possession of a building;
       "occupation of a building without a certificate of occupancy
       is illegal" [syn: occupation, occupancy, moving in]

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "occupancy":
   abiding, abode, adverse possession, alodium, burgage, claim,
   cohabitation, colony, commorancy, de facto, de jure, dependency,
   derivative title, dwelling, fee fief, fee position, fee simple,
   fee simple absolute, fee simple conditional, fee simple defeasible,
   fee simple determinable, fee tail, feodum, feud, fiefdom,
   frankalmoign, free socage, freehold, gavelkind, habitancy,
   habitation, having title to, hold, holding, inhabitancy,
   inhabitation, inhabiting, knight service, lay fee, lease,
   leasehold, legal claim, legal possession, living, lodging, mandate,
   nesting, occupation, original title, owning, possessing,
   possession, preoccupancy, preoccupation, prepossession,
   prescription, property, property rights, proprietary rights,
   residence, residency, residing, seisin, settlement, socage,
   sojourning, squatting, staying, staying over, stopping, sublease,
   tenancy, tenantry, tenure, tenure in chivalry, title, underlease,
   undertenancy, usucapion, villein socage, villeinhold, villenage