millennialist

noun pl. millenniums or millennia

1. any period of 1,000 years: 2000 through 1001 is the 2d millennium
2. 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
3. a 1,000th anniversary or its commemoration
4. any period of great happiness, peace, prosperity, etc.; imagined golden age