"millennia" in the noun sense
1. millennium, millenary
a span of 1000 years
2. millennium
New Testament) in Revelations it is foretold that those faithful to Jesus will reign with Jesus over the earth for a thousand years the meaning of these words have been much debated some denominations (e.g. Jehovah's Witnesses) expect it to be a thousand years of justice and peace and happiness
3. millennium, millenary
the 1000th anniversary (or the celebration of it)
Source: WordNet® (An amazing lexical database of English)
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