The Collaborative International Dictionary of English v.0.48:

Preconception \Pre`con*cep"tion\, n.
   The act of preconceiving; conception or opinion previously
   formed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

preconception
    n 1: 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]
    2: a partiality that prevents objective consideration of an
       issue or situation [syn: bias, prejudice,
       preconception]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "preconception":
   assumption, bent, bias, delusion, favoritism, forejudgment,
   idee fixe, illusion, inclination, jaundice, jaundiced eye, leaning,
   one-sidedness, parti pris, partialism, partiality, partisanship,
   preapprehension, preconclusion, preconsideration, predecision,
   predetermination, predilection, predisposition, prejudgment,
   prejudication, prejudice, premature judgment, prenotion,
   prepossession, presumption, presupposal, presupposition,
   presurmise, twist, undetachment, undispassionateness