ETYM Late Lat., from Latin mille a thousand + annus a year. Related to Mile, and Annual.
1. The 1000th anniversary.
2. A span of 1000 years.
3. (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.
Period of one thousand years; thousandth anniversary; future period of ideal happiness on earth, especially that foretold in Revelations XX. Period of 1,000 years. Some quasi-Christian sects, such as Jehovah's Witnesses, believe that Jesus will return to govern the Earth in person at the next millennium, the 6001st year after the creation (as located by Archbishop Usher at 4004 BC).
This belief, millenarianism, also called chiliasm (from the Greek for 1,000), was widespread in the early days of Christianity. As hopes were disappointed, belief in the imminence of the second coming tended to fade, but millenarian views have been expressed at periods of great religious excitement, such as the Reformation.