mil·len·ni·um 
(mə-lĕnē-əm)
(mə-lĕnē-əm)n. pl. mil·len·ni·a (-lĕnē-ə) or mil·len·ni·ums
1. A span of one thousand years.
2. A thousand-year period of holiness mentioned in the book of Revelation, during which Jesus and his faithful followers are to rule on earth.
3. A hoped-for period of joy, serenity, prosperity, and justice.
4. A thousandth anniversary.
[New Latin mīllennium : Latin mīlle, thousand; see gheslo- in the Appendix of Indo-European roots + Latin annus, year; see at- in the Appendix of Indo-European roots.]