momentous

adjective

mo·​men·​tous mō-ˈmen-təs 

mə-

: having great or lasting importance : consequential, significant

a momentous decision

a momentous event/occasion

The Senate begins a momentous debate on health care today …

—The New York Times

Deydey usually talked about his travels, the places he'd seen and the people, the close calls and momentous encounters with animals, weather, other Anishinabeg, and best of all, ghosts.

—Louise Erdrich

The late nineteenth century was strewn with inventions. Many were momentous, but few affected men and women more closely than the bicycle and its motorized offspring: motorcycle, motor-car and aeroplane.

—Eugen Weber

momentously adverb

a momentously important decision

… a … twist that is executed differently from the comic book story, but is just as dramatically and momentously presented.

—The Philippines Daily Inquirer

momentousness noun

But other East Europeans had little time to marvel at the momentousness of the moment. Just one day after the fall of the [Berlin] Wall, Bulgaria's dour leader of 35 years, Todor Zhivkov, was ousted.

—Stephen E. Deane

Synonyms

• big
• consequential
• earth-shattering
• earthshaking
• eventful
• historic
• important
• major
• material
• meaningful
• monumental
• much
• significant
• substantial
• tectonic
• weighty

Examples of momentous in a Sentence

My college graduation was a momentous day in my life.

a momentous occasion that will go down in the history books

Recent Examples on the Web

Harvey Frommer, a sports historian and reporter, puts the tale of that momentous game together using oral history, gathered from hundreds of interviews with players, coaches, media and spectators alike. —Sophie Hanson, StyleCaster, 9 Feb. 2025

From the start, even during warmups, the 6-foot-7 senior forward realized a perfect emotional and physical backdrop that would end up foreshadowing a momentous performance. —Patrick Z. McGavin, Chicago Tribune, 5 Feb. 2025

It's been a momentous year for Tracy Otto and her fiancé Ricky Riessle! —Rachel Flynn, People.com, 28 Jan. 2025

The following predictions for major developments (on the field and off) are partly intended to make the Hotline look brilliant but mostly designed to prepare fans for what could be a momentous year in college sports. —Jon Wilner, The Mercury News, 27 Jan. 2025

Word History

First Known Use

1631, in the meaning defined above

Kids Definition

momentous

adjective

mo·​men·​tous mō-ˈment-əs 

: very important

a momentous decision

momentously adverb