millennium

noun3

1. •
   A period of time consisting of one thousand years.

   • How this happens no one really knows, despite the efforts of philosophers and psychologists over two and a half millennia to study the phenomenon. — 1972
2. •
   The year in which one period of one thousand years ends and another begins, especially the year 2000.

   • A huge fireworks display was put on in Sydney to celebrate the millennium.
3. •
   (no longer used) Any long (and possibly endless) era of universal happiness, peace, and prosperity, predicted by various people to come about someday.

   • When rumour got afoot that in future mechanical power would be unlimited, the people expected a millennium. — 1930