confidence has 6 distinct synonyms spread across 2 of its 5 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. Its one recorded opposite is diffidence.
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.
freedom from doubt; belief in yourself and your abilities
“his assurance in his superiority did not make him popular”
a feeling of trust (in someone or something)
“I have confidence in our team”
a state of confident hopefulness that events will be favorable
“public confidence in the economy”
a secret that is confided or entrusted to another
“everyone trusted him with their confidences”
Synonyms, antonyms and the broader and narrower relations for confidence come from Princeton University’s WordNet. Full sources and licences.