millennium

n. [ LL., fr. L. mille a thousand + annus a year. See Mile, and Annual. ] 1. A period of one thousand years. [ 1913 Webster ]

2. Specifically: The period of a thousand years mentioned 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. [ 1913 Webster ]

3. Hence: A long period of happiness, righteousness, and prosperity, usually considered as being in the indefinite future. [ PJC ]

4. A thousandth anniversary; especially, Each first day of January falling in a year which is a multiple of one thousand, such as in 1000 a. d. or 2000 a. d.; as, the second millenium will be celebrated on January 1, 2000; also used attributively, as a millenium celebration. Technically, if the calendar of the Common Era (Anno Domini) is considered as beginning on January 1, 1 a. d., then the millenium will fall in each year ending in 001, as in 1001 a. d. or January 1, 2001 a. d.. However in the common culture, the change of the first digit of the year from 1 to 2, as from 1999 to 2000 is considered as the more symbolic event, especially since the dating of the beginning of the Christian era is somewhat arbitrary, having been an attempt to fix the date of the birth of Christ, and being considered by scholars as being in error by as much as five years. [ PJC ]