English Reference

Word

millennium

Phoneticsmil·len·ni·um

US/məˈɫɛniəm/

UK/mɪlˈɛniəm/

Definitions

01one thousand years

B2

n. a period of one thousand years.

n. a span of time consisting of one thousand years.

“The ancient castle has stood for nearly a millennium.”

“Archaeologists discovered evidence of a civilization that had thrived for over a millennium before suddenly vanishing from the historical record.”

Usage

The plural form can be either 'millenniums' or the more formal 'millennia'.

Pitfall

The millenium was celebrated in 2000.

The millennium was celebrated in 2000.

Millennium is frequently misspelled; remember it has a double 'l' and a double 'n'.

Teaching tip

In academic writing, 'millennia' is the preferred plural form.

02the year 2000

B2

n. the specific time when one thousand-year period ends and another begins, especially the year 2000.

n. the anniversary or transition point marking the end of one thousand-year cycle and the start of the next.

“Many people were worried about computer errors at the turn of the millennium.”

“The celebrations for the new millennium were marked by spectacular firework displays in major cities across the globe.”

Usage

Usually used with the definite article 'the'.

03an era of peace

C2 · Religion

n. a long period of time in the future when everyone will be happy and peaceful.

n. a hoped-for period of joy, serenity, and prosperity; often used in a religious or utopian context.

“The poet wrote about a coming millennium where war would no longer exist.”

“The philosopher's vision of a secular millennium relied on the triumph of reason over tribalism.”

Literary · Archaic

Teaching tip

This sense is rare in modern conversation and is mostly found in older literature or religious texts.

Synonyms

Real-World Examples

“The chemistry of the corals revealed that El Niño events from the past 40 years were stronger than at any other time sampled in the past millennium.”
Phys.org · 28 Aug 2026
“Based on the picture the data present, Schulz Paulsson believes that the megaliths were first constructed by dwellers of northwest France during the second half of the fifth millennium BC.”
Smithsonian Magazine · 11 Feb 2019
“A second serving of a year-best pop album: a puckish hyperpop take on the acoustic guitar-addled pop of the early millennium, with a cataclysmic, Vegas-ready outro for good measure.”
The Guardian · 28 Aug 2026

Etymology

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

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

millennialAdjectivemillenniumNoun

This entry

Level
B2 · Upper Intermediate
Frequency
Frequent
Updated

Scan code

englishreference.com/q/millennium

English Reference