The Collaborative International Dictionary of English v.0.48:

Ideology \I`de*ol"o*gy\, n. [Ideo- + -logy: cf. F.
   id['e]ologie.]
   1. The science of ideas. --Stewart.
      [1913 Webster]

   2. (Metaph.) A theory of the origin of ideas which derives
      them exclusively from sensation.
      [1913 Webster]

   Note: By a double blunder in philosophy and Greek,
         id['e]ologie . . . has in France become the name
         peculiarly distinctive of that philosophy of mind which
         exclusively derives our knowledge from sensation. --Sir
         W. Hamilton.

   3. A set or system of theories and beliefs held by an
      individual or group, especially about sociopolitical goals
      and methods to attain them; in common usage, ideology is
      such a set of beliefs so strongly held by their adherents
      as to cause them to ignore evidence against such beliefs,
      and thus fall into error -- in this sense it is viewed as
      a negative trait; contrasted to pragmatism, and distinct
      from idealism.
      [PJC]

WordNet (r) 3.0 (2006):

ideology
    n 1: an orientation that characterizes the thinking of a group
         or nation [syn: political orientation, ideology,
         political theory]
    2: imaginary or visionary theorization

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "ideology":
   Weltanschauung, articles of religion, body of ideas, catechism,
   climate, climate of opinion, credenda, credo, creed, cult,
   doctrinal statement, doctrine, dogma, ethos, faith,
   formulated belief, gospel, intellectual climate, ism,
   moral climate, mores, norms, philosophy, political faith,
   political philosophy, principles, religion, school,
   spiritual climate, system of belief, system of ideas,
   system of theories, tenets, world view