Etymology
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fiduciary (adj.)

1640s, "holding something in trust," from Latin fiduciarius "entrusted, held in trust," from fiducia "trust, confidence, reliance;" in law, "a deposit, pledge, security," from root of fidere "to trust" (from PIE root *bheidh- "to trust, confide, persuade"). In Roman law, fiducia was "a right transferred in trust;" paper currency sense (1878) is because its value depends on the trust of the public. As a noun, "one who holds something in trust," from 1630s.

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fiducial (adj.)

1570s, "assumed as a fixed basis for comparison," from Latin fiducialis "reliable," from fiducia "trust" (from PIE root *bheidh- "to trust, confide, persuade"). From 1620s as "pertaining to trust;" 1832 as "fiduciary."

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