boulder
noun
a detached and rounded or worn rock, especially a large one.
boulder
1 American
[bohl-der]
/ ˈboʊl dər /
Or
bowlder
noun
-
boulders
plural
Boulder
2
American
[bohl-der]
/ ˈboʊl dər /
noun
boulder
British
/ ˈbəʊldə /
noun
-
a smooth rounded mass of rock that has a diameter greater than 25cm and that has been shaped by erosion and transported by ice or water from its original position
-
geology a rock fragment with a diameter greater than 256 mm and thus bigger than a cobble
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Etymology
Origin of boulder
1610–20; short for boulder stone; Middle English bulderston < Scandinavian; compare dialectal Swedish bullersten big stone (in a stream), equivalent to buller rumbling noise (< Old Swedish bulder ) + sten stone
Explanation
A boulder is a rock — a big one. Scientists often think of a boulder in more technical terms than we do. They use the word to describe not just a big rock, but a rock that some natural force — a river, a glacier or the like — has moved from its original location to its present one. A good way to remember all this is to think of Boulder, a city in Colorado that stands in the middle of the Rocky Mountains, and is, no doubt, full of boulders.
Vocabulary lists containing boulder
"Mending Wall," by Robert Frost
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Earth Science - Middle School
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Earth Science - High School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
Homeowners in Dana Point are working to install emergency protection from the onslaught of waves, including a boulder barrier, according to the statement from the city.
From Los Angeles Times ● Sep. 10, 2026
Company dancer Lloyd Knight, costumed as the Preacher in “Spring” and captured in a determined stance on a boulder, faces the book’s last page, which quotes Graham: “Dancers are the messengers of the gods.”
From The Wall Street Journal ● Jun. 9, 2026
"It was just timing. The boulder that actually took Jack, it could have gone in a week's time, a year's time - it just happened to go then and there."
From BBC ● May 26, 2026
Larger incoming objects, such as boulder sized rocks that create especially bright flashes, are known as bolides or fireballs.
From Science Daily ● May 14, 2026
A gap in the fog had given her a clear view: she’d seen the stream rushing past a clump of spruce, and a big dark boulder hunched beside them.
From "Wolf Brother" by Michelle Paver
Visitors at Boulder Beach would stumble on human remains on three different occasions from July to August 2022 that authorities said all belonged to the same person, Claude Russell Pensinger, a Las Vegas resident.
From Los Angeles Times ● Aug. 19, 2026
Boulder, which the justices will hear in their fall term.
From The Wall Street Journal ● Jul. 27, 2026
The Warwick team, working with astronomers from the University of Colorado Boulder in the US, was interested in the four nearby systems because of a "substantial radial wobble".
From BBC ● Jul. 14, 2026
The University of Arizona in Tucson operates the HiRISE camera, which was built by BAE Systems in Boulder, Colorado.
From Science Daily ● Jul. 14, 2026
Everything in East Hampden was dark and deserted, even the Boulder Tap; the only light for miles around seemed to be the light shimmering around the pay phone in front.
From "The Secret History" by Donna Tartt
As the waves bashed the coast this week, boulders smashed into the piles of Mitchell Leib’s Malibu home, plucking them like a “guitar string” and shaking his house.
From Los Angeles Times ● Sep. 11, 2026
Then it gathers shape and speed: water, mud, boulders, ice and rock surging down the valley.
From BBC ● Sep. 1, 2026
Photographs shared by the disaster office showed workers wading through churned mud and navigating vast boulders left by the floods.
From Barron's ● Aug. 30, 2026
Its stone fireplace comes to rest on what appear to be colossal boulders deposited by the last vagabond glacier.
From The Wall Street Journal ● Aug. 28, 2026
And the boulders peeking out from the lapping waves remind me of polished onyx.
From "The Sea in Winter" by Christine Day
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
