millennium

noun

mil·​len·​ni·​um mə-ˈle-nē-əm 

plural millennia mə-ˈle-nē-ə  or millenniums

1

a

: the thousand years mentioned in the book of Revelation (see revelation sense 3) in the Christian Bible during which holiness is to prevail and Christ is to reign on earth

b

: a period of great happiness or human perfection

2

a

: a period of 1000 years

especially : one reckoned from the beginning of the Christian era

at the start of the third millennium

b

: a 1000th anniversary or its celebration

In 2015 the city of Leipzig, Germany, celebrated its millennium.

Did you know?

Since in Latin mille means "thousand", a millennium lasts 1,000 years. Thus, we're living today at the beginning of the third millennium since the birth of Christ. But some religious sects, relying on a prophecy in the biblical Book of Revelation, speak of a coming millennium when Jesus will return to reign on earth for 1,000 years, evil will be banished, and all will live in peace and happiness. Members of these sects who keep themselves in a constant state of preparedness are called millenarians or millennialists.

Examples of millennium in a Sentence

The book describes the changes that have occurred in the landscape over many millennia.

The year 2000 was celebrated as the beginning of the third millennium.

Recent Examples on the Web

Returning to the core of his talk, Yanxiao likened the Xiongnu’s impact on the West to that of the Mongols, who, a millennium later, would alter the cultural topology of Eurasia. —Chang Che, New Yorker, 8 Mar. 2026

In the new millennium, Jones continued driving, at one point for Uber, and now for HopSkipDrive, transporting kids to school. —Greg Poole, Rolling Stone, 5 Mar. 2026

But harsher challenges would present in the new millennium. —Edward Lotterman, Twin Cities, 1 Mar. 2026

Our very own Karissa Waddick talked to Ricker about the time capsule and how all 50 states will contribute to it, where it will be placed and how it'll be constructed to keep its contents safe for a quarter-millennium. —Phaedra Trethan, USA Today, 27 Feb. 2026

Word History

Etymology

New Latin, from Latin mille thousand + New Latin -ennium (as in biennium)

First Known Use

circa 1638, in the meaning defined at sense 1a

Phrases Containing millennium

• the millennium

Rhymes for millennium

• biennium
• quinquennium
• triennium

Kids Definition

millennium

noun

mil·​len·​ni·​um mə-ˈlen-ē-əm 

plural millennia

-ē-ə

or millenniums

1

a

: a period of 1000 years

b

: a 1000th anniversary or its celebration

2

: a period of great happiness

millennial

-ē-əl

adjective