The Collaborative International Dictionary of English v.0.48:

Fiducial \Fi*du"cial\, a. [L. fiducia trust, confidence; akin to
   fides faith. See Faith.]
   1. Having faith or trust; confident; undoubting; firm.
      "Fiducial reliance on the promises of God." --Hammond.
      [1913 Webster]

   2. Having the nature of a trust; fiduciary; as, fiducial
      power. --Spelman.
      [1913 Webster]

   Fiducial edge (Astron. & Surv.), the straight edge of the
      alidade or ruler along which a straight line is to be
      drawn.

   Fiducial line or Fiducial point (Math. & Physics.), a
      line or point of reference, as for setting a graduated
      circle or scale used for measurements.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fiducial
    adj 1: relating to or of the nature of a legal trust (i.e. the
           holding of something in trust for another); "a fiduciary
           contract"; "in a fiduciary capacity"; "fiducial power"
           [syn: fiduciary, fiducial]
    2: used as a fixed standard of reference for comparison or
       measurement; "a fiducial point"
    3: based on trust

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "fiducial":
   balanced, convictional, cool, fast, fiduciary, firm,
   firm as Gibraltar, imperturbable, in equilibrium, pistic,
   predictable, reliable, secure, solid, sound, stable, steadfast,
   steady, substantial, unflappable, unflinching, unshakable,
   unwavering, well-balanced, without nerves