fi·du·ci·ar·y 
(fĭ-dshē-ĕr′ē, -shə-rē, -dy-, fī-)
(fĭ-dshē-ĕr′ē, -shə-rē, -dy-, fī-)adj.
1.
a. Of or relating to a duty of acting in good faith with regard to the interests of another: a company's fiduciary responsibility to investors.
b. Of or being a trustee or trusteeship.
c. Held in trust.
2. Of or consisting of fiat money.
3. Of, relating to, or being a system of marking in the field of view of an optical instrument that is used as a reference point or measuring scale.
n. pl. fi·du·ci·ar·ies
One, such as an agent of a principal or a company director, who has a duty of acting in good faith with regard to the interests of another.
[Latin fīdūciārius, from fīdūcia, trust; see FIDUCIAL.]