momentous

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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

momentousness

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noun

mo·​men·​tous·​ness

plural -es

: the quality or state of being momentous

impress his visitors with the momentousness … of all he had to say

—H. V. Gregory

Synonyms of momentous

Adjective

• major
• important
• significant
• historic
• big

Examples of momentous in a Sentence

Adjective

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

Adjective

And such momentous changes as bringing back Eric Bieniemy as offensive coordinator and the Chiefs signing Super Bowl MVP Kenneth Walker III to revive their running game heralded Reid’s recognition of the moment. — Vahe Gregorian july 31, Kansas City Star, 31 July 2026

The sleepy new Strokes album Reality Awaits landed Friday, less than a week before the 25th anniversary of the band’s momentous 2001 debut, Is This It. — Craig Jenkins, Vulture, 28 July 2026

The Slovenian began arguably cycling’s most famous climb more than three minutes down on remnants of the breakaway but ascended it in a time of 35 minutes and 27 seconds — one of the most momentous performances the sport has witnessed. — Jacob Whitehead, New York Times, 24 July 2026

Ronstadt’s career, too, was set to take more momentous turns. — Rance Collins, Entertainment Weekly, 15 July 2026

Word History

First Known Use

Adjective

1631, in the meaning defined above

Rhymes for momentous

• apprentice
• placentas
• portentous
• filamentous
• ligamentous
• mentis
• prentice

Kids Definition

momentous

adjective

mo·​men·​tous mō-ˈment-əs 

: very important

a momentous decision

momentously adverb