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

• major
• important
• significant
• historic
• big

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

For the second year in a row, the 4th of July played host to a momentous musical release; coincidentally, the consecutive drops have come from the two guys who had the biggest rap beef of all time last year, Drake and Kendrick Lamar. —Armon Sadler, VIBE.com, 7 July 2025

Always this sense of momentous occasion for a challenge with diminishing returns and our perpetual disappointment? —Chris Feil, Vulture, 4 July 2025

The Eras Tour is receiving a different momentous honor, but the timing is just too perfect. —Bryan West, The Tennessean, 2 July 2025

Climate comparison Given how momentous the conclusive discovery of extraterrestrial life would be, these assumptions mean that many scientists err on the side of caution. —Oliver Swainston, Space.com, 28 June 2025

Word History

First Known Use

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