The Collaborative International Dictionary of English v.0.48:

Transcendentalism \Tran`scen*den"tal*ism\, n. [Cf. F.
   transcendantalisme, G. transcendentalismus.]
   1. (Kantian Philos.) The transcending, or going beyond,
      empiricism, and ascertaining a priori the fundamental
      principles of human knowledge.
      [1913 Webster]

   Note: As Schelling and Hegel claim to have discovered the
         absolute identity of the objective and subjective in
         human knowledge, or of things and human conceptions of
         them, the Kantian distinction between transcendent and
         transcendental ideas can have no place in their
         philosophy; and hence, with them, transcendentalism
         claims to have a true knowledge of all things, material
         and immaterial, human and divine, so far as the mind is
         capable of knowing them. And in this sense the word
         transcendentalism is now most used. It is also
         sometimes used for that which is vague and illusive in
         philosophy.
         [1913 Webster]

   2. Ambitious and imaginative vagueness in thought, imagery,
      or diction.
      [1913 Webster]

WordNet (r) 3.0 (2006):

transcendentalism
    n 1: any system of philosophy emphasizing the intuitive and
         spiritual above the empirical and material [syn:
         transcendentalism, transcendental philosophy]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "transcendentalism":
   eeriness, elfdom, faerie, miraculousness, mysteriousness, mystery,
   numinousness, otherworldliness, preternaturalism, superhumanity,
   supernaturalism, supernaturality, supernaturalness, supernature,
   supernormalness, superphysicalness, supersensibleness,
   supranaturalism, supranature, the occult, the supernatural,
   the supersensible, unearthliness, unworldliness, witchery