fiducial has 1 distinct synonym spread across 1 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
relating to or of the nature of a legal trust (i.e. the holding of something in trust for another)
“a fiduciary contract”
2 of the 3 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for fiducial.
Synonyms, antonyms and the broader and narrower relations for fiducial come from Princeton University’s WordNet. Full sources and licences.