millennium (millenniums plural) (millennia plural )
1 n-count A millennium is a period of one thousand years, especially one which begins and ends with a year ending in `000', for example the period from the year 1000 to the year 2000.
FORMAL
2 n-sing Many people refer to the year 2000 as the Millennium.
usu the N, N n
...the eve of the Millennium.