authority has 16 distinct synonyms spread across 4 of its 7 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.
the power or right to give orders or make decisions
“he has the authority to issue warrants”
(usually plural) persons who exercise (administrative) control over others
“the authorities have issued a curfew”
an expert whose views are taken as definitive
“he is an authority on corporate law”
freedom from doubt; belief in yourself and your abilities
“his assurance in his superiority did not make him popular”
an administrative unit of government
“the Central Intelligence Agency”
official permission or approval
“authority for the program was renewed several times”
Synonyms, antonyms and the broader and narrower relations for authority come from Princeton University’s WordNet. Full sources and licences.