Home › Words › M › millionenniummillionenniummillionennium means synonym of mega-annum: a period of time consisting of one million years.Among words judged in Lexicurio's Arena, millionennium ranks #2,710 of 42,752 for Qualifying.EtymologyBlend of million + millennium.nounSynonym of mega-annum: a period of time consisting of one million years.e.g.“Holonym: eternity”Definitions & examples from Wiktionary (CC BY-SA 3.0).