Eonian is a rare word that means 'eternal' or 'lasting forever.' Some synonyms for eonian include 'everlasting,' 'perennial,' 'timeless,' 'immortal,' and 'endless.' These words convey the same sentiment of something lasting forever or being eternal. Other possible synonyms for eonian could include 'infinite,' 'unlimited,' 'interminable,' 'unceasing,' or 'eternal.' These words can be used interchangeably with eonian in writing, literature, or other creative contexts. Overall, eonian and its synonyms are used to describe something that lasts beyond time, or that exists independent of time.