Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

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

   {Fiducial} {line or point} (Math. & Physics.), a line or
      point of reference, as for setting a graduated circle or
      scale used for measurments.