inaugural has 6 distinct synonyms spread across 3 of its 4 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 exaugural.
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.
an address delivered at an inaugural ceremony (especially by a United States president)
the ceremonial induction into a position
“the new president obviously enjoyed his inauguration”
Synonyms, antonyms and the broader and narrower relations for inaugural come from Princeton University’s WordNet. Full sources and licences.
occurring at or characteristic of a formal investiture or induction
“the President's inaugural address”