The Collaborative International Dictionary of English v.0.48:

Prepossession \Pre`pos*ses"sion\, n.
   [1913 Webster]
   1. Preoccupation; prior possession. --Hammond.
      [1913 Webster]

   2. Preoccupation of the mind by an opinion, or impression,
      already formed; preconceived opinion; previous impression;
      bias; -- generally, but not always, used in a favorable
      sense; as, the prepossessions of childhood. "The
      prejudices and prepossessions of the country." --Sir W.
      Scott.
      [1913 Webster]

   Syn: Bent; bias; inclination; preoccupancy; prejudgment. See
        Bent.
        [1913 Webster]

WordNet (r) 3.0 (2006):

prepossession
    n 1: the condition of being prepossessed; "the king's
         prepossession in my favor is very valuable"
    2: an opinion formed beforehand without adequate evidence; "he
       did not even try to confirm his preconceptions" [syn:
       preconception, prepossession, parti pris, preconceived
       opinion, preconceived idea, preconceived notion]

Moby Thesaurus II by Grady Ward, 1.0:

139 Moby Thesaurus words for "prepossession":
   adoption, adverse possession, affinity, alodium, appropriation,
   arrogation, assumption, bag, bent, bias, burgage, chosen kind,
   claim, colonization, colony, complex, compulsion, conquest,
   cup of tea, de facto, de jure, dependency, derivative title,
   druthers, enslavement, fancy, fascination, favor, favoritism,
   fee fief, fee position, fee simple, fee simple absolute,
   fee simple conditional, fee simple defeasible,
   fee simple determinable, fee tail, feodum, feud, fiefdom, fixation,
   fixed idea, forejudgment, frankalmoign, free socage, freehold,
   gavelkind, hang-up, having title to, hold, holding, hypercathexis,
   idee fixe, inclination, indent, irresistible impulse, jaundice,
   jaundiced eye, knight service, lay fee, leaning, lease, leasehold,
   legal claim, legal possession, mandate, monomania, morbid drive,
   obsession, obsessive compulsion, occupancy, occupation,
   one-sidedness, original title, owning, parti pris, partialism,
   partiality, particular choice, partisanship, personal choice,
   possessing, possession, preapprehension, preconception,
   preconclusion, preconsideration, predecision, predetermination,
   predilection, predisposition, preemption, preference, prejudgment,
   prejudication, prejudice, premature judgment, prenotion,
   preoccupancy, preoccupation, prescription, presumption,
   presupposal, presupposition, presurmise, proclivity, property,
   property rights, proprietary rights, requisition, ruling passion,
   seisin, socage, squatting, style, subjugation, sublease, takeover,
   taking over, taste, tenancy, tenantry, tendency, tenure,
   tenure in chivalry, thing, tic, title, twist, type, underlease,
   undertenancy, undetachment, undispassionateness, usucapion,
   usurpation, villein socage, villeinhold, villenage