Definition of "millennium"

The first known man-made tools, including spear points and axes, were associated with a hunting and gathering pattern that lasted, according to anthropologists, almost 200 millennia.

2013, Al Gore, The Future: Six Drivers of Global Change‎, New York: Random House, page 37

Magnolias are some of the most primitive of our flowering trees, and fossils dating back millennia prove that they have had little need to evolve.

2013 March 24, Dan Pearson, The Guardian

After the purifying judgments which attended the personal return of Christ to the Earth, He will reign over restored Israel and over the earth for one thousand years. This is the period commonly called the Millennium. The seat of His power will be Jerusalem, and the saints, including the saved of the Dispensation of Grace, viz., the Church, will be associated with Him in His glory.

1888, C. I. Scofield, “The Seven Dispensations”, in Rightly Dividing the Word of Truth (2 Tim. 2:15): Ten Outline Studies of The More Important Divisions of Scripture‎, Second edition (Religion), Philadelphia, Penn.: Philadelphia School of the Bible, published 1923, page 25

An archangel ecstatically proclaiming the Millennium, and then finding that it clashed unpardonably with Henley and would have to be indefinitely postponed, could hardly have felt more crestfallen than Cornelius Appin at the reception of his wonderful achievement.

1911, Saki, “Tobermory”, in The Chronicles of Clovis

the end of the world would be heralded by a series of spectacular and symbolic events […]. According to most commentators, this millennium had already begun.

1971, Keith Thomas, Religion and the Decline of Magic, Folio Society, published 2012, page 137

Conrad's later years unfolded in the shadow of the coming Millennium, when the end of the world was forecast.

2011, Norman Davies, Vanished Kingdoms, Penguin, published 2012, page 117

But the aggressive members of society are always tending to become bullies, robbers, and swindlers; and no one believes that such a state of things as we now live in is the millennium.

1902, William James, The Varieties of Religious Experience, Folio Society, published 2008, page 318