fiducial

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 ]