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

With the latest Antarctic ice core, scientists hope to learn how levels of greenhouse gases have changed over millennia. —Sarah Kuta, Smithsonian Magazine, 10 Jan. 2025

Old trees may have grown through entire millennia that were wetter than the past 20 years. —Alana Chin, The Conversation, 9 Jan. 2025

The researchers analyzed three ice cores and found that lead concentrations rose and fell over roughly a millennium in ways that corresponded to key events in Rome’s economic history. —Evan Bush, NBC News, 7 Jan. 2025

The atmospheric lead pollution levels seen after 15 B.C. were not exceeded again until the early 2nd millennium during the High Middle Ages. —Kevin Lynn, Newsweek, 6 Jan. 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

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