eventful has 1 distinct synonym spread across 1 of its 2 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 uneventful.
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.
full of events or incidents
“the most exhausting and eventful day of my life”
having important issues or results
“the year's only really consequential legislation”
Synonyms, antonyms and the broader and narrower relations for eventful come from Princeton University’s WordNet. Full sources and licences.