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 Revelation (see revelation sense 3) 20 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

The location has housed a succession of restaurants, starting with a Bennigan’s at the dawn of the new millennium. —Robert Channick, Chicago Tribune, 21 June 2025

Gap was one of the most popular retail names of the 1980s and 1990s, but fell out of favor among consumers at the start of the new millennium. —Ryan Baker, CNBC, 14 June 2025

During the first decade of the new millennium, before the rise of Musical.ly and then TikTok, television still dominated the attention of young children. —ArsTechnica, 11 June 2025

Gin, a spirit that can trace its origins back to the Middle Ages, has seen a surge of interest in the new millennium. —Hudson Lindenberger, Forbes.com, 3 June 2025

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