The Collaborative International Dictionary of English v.0.48:

Superstitious \Su`per*sti"tious\, a. [F. superstitieux, L.
   superstitiosus.]
   1. Of or pertaining to superstition; proceeding from, or
      manifesting, superstition; as, superstitious rites;
      superstitious observances.
      [1913 Webster]

   2. Evincing superstition; overscrupulous and rigid in
      religious observances; addicted to superstition; full of
      idle fancies and scruples in regard to religion.
      [1913 Webster]

            Ye men of Athens, I perceive that in all things ye
            are too superstitious.                --Acts xvii.
                                                  22.
      [1913 Webster]

   3. Overexact; scrupulous beyond need.
      [1913 Webster]

   Superstitious use (Law), the use of a gift or bequest, as
      of land, etc., for the maintenance of the rites of a
      religion not tolerated by the law. [Eng.] --Mozley & W.
      [1913 Webster] -- Su`per*sti"tious*ly, adv. --
      Su`per*sti"tious*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

superstitious
    adj 1: showing ignorance of the laws of nature and faith in
           magic or chance; "finally realized that the horror he
           felt was superstitious in origin"

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "superstitious":
   credulous, doting, easily taken in, easy of belief, fond,
   inclined to believe, infatuated, overconfiding, overcredulous,
   overtrustful, overtrusting, trustful, trusting, uncritical,
   undoubting, unskeptical, unsuspecting, unsuspicious