millennium

Amillennium is a period of 1000 years or is an anniversary of the passage of 1000 years. (noun)

See millennium in Webster's New World College Dictionary

any period of 1,000 years: 2000 through 1001 is the 2d millennium
a period of 1,000 years reckoned from a certain time, esp. from the beginning of the Christian Era (1): the year A.D. 2001 marks the beginning of the third millennium
a 1,000th anniversary or its commemoration
any period of great happiness, peace, prosperity, etc.; imagined golden age

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See millennium in American Heritage Dictionary 4

(mə-lĕnˈē-əm)

noun pl. mil·len·ni·a (-lĕnˈē-ə) or mil·len·ni·ums

A span of one thousand years.
A thousand-year period of holiness mentioned in Revelation 20, during which Jesus and his faithful followers are to rule on earth.
A hoped-for period of joy, serenity, prosperity, and justice.
A thousandth anniversary.

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