millennium

n. unit of time equal to one thousand years; period of one thousand years; thousandth year anniversary

A millennium (pl. millennia) is a period of time equal to one thousand years (from Latin , thousand, and , year). The term may implicitly refer to calendar millennia; periods tied numerically to a particular dating system, specifically ones that begin at the starting (initial reference) point of the calendar in question (typically the year 1) or in later years which are whole number multiples of a thousand years after it.
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Noun
1. a span of 1000 years
(hypernym) time period, period of time, period
(part-meronym) century
2. (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
(hypernym) doctrine, philosophy, philosophical system, school of thought, ism
(classification) New Testament
3. the 1000th anniversary (or the celebration of it)
(hypernym) anniversary, day of remembrance

n. millennium, unit of time equal to one thousand years; thousandth year anniversary

(n.)
A thousand years; especially, the thousand years mentioned in the twentieth chapter in the twentieth chapter of Revelation, during which holiness is to be triumphant throughout the world. Some believe that, during this period, Christ will reign on earth in person with his saints.