the.com/fiduciary

means A person or institution legally and ethically bound to act in someone else's best financial interest rather than their own.

from From Latin 'fiducia,' meaning trust or confidence, itself rooted in 'fidere,' to trust. The word entered legal English in the 1700s to describe relationships — like trustee and beneficiary — built entirely on that trust, where one party holds power over another's money or property and is bound by law to use it faithfully rather than selfishly.