Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
millennian is an adjective meaning "relating to a millennium or span of a thousand years". It carries one recorded sense.
relating to a millennium or span of a thousand years
Definitions, synonyms and semantic relations for millennian come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.