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

India’s ambassador to Indonesia, Sandeep Chakravorty, said the Ramayana and the Mahabharata had been part of Indonesian temple culture, wayang (traditional puppet theater) and the popular imagination for over a millennium. — Naman Ramachandran, Variety, 25 Oct. 2026

The result, in both its grace notes and its gestalt, freakishly summons the placeless, timeless, sunless anti-aesthetics of a turn-of-the-millennium strip-mall buffet. — Helen Rosner, New Yorker, 25 Oct. 2026

The familiar imperial arc—expansion, overreach, strain, unraveling—once played out across a century or even a millennium. — Niall Ferguson, Foreign Affairs, 20 Oct. 2026

Founded in Seattle in 1999, on the cusp of Y2K and a new millennium, the jeweler was among the first to take diamond shopping online. — Lilah Ramzi, Vogue, 15 Oct. 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

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