Meaning

noun a span of 1000 years

noun (New Testament) in Revelations it is foretold that those faithful to Jesus will reign with Jesus over the earth for a thousand years; the meaning of these words have been much debated; some denominati

noun the 1000th anniversary (or the celebration of it)

originFrom Late Latin mīllennium, from Latin mīllennis (“1000-year”) + -ium (forming abstract nouns).

Etymology from Wiktionary, CC BY-SA 3.0