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
Glassock describes the facilitator’s job as pushing a boulder: “It’s hardest when it’s yet to move,” he said.
From The Wall Street Journal ● Aug. 4, 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
Only the man who had fallen off the boulder needed to be carried back to Sister Gladys’s hospital, and to be on the safe side a litter was used for Baba Joseph as well.
From "A Girl Named Disaster" by Nancy Farmer
In August, human remains, including a jawbone with teeth and dental fillings and rib bones, were discovered at Boulder Beach in the Lake Mead National Recreation Area.
From Los Angeles Times ● Oct. 16, 2026
Another question for Boulder County: What energy sources does the county use to power its facilities and vehicle fleet?
From The Wall Street Journal ● Oct. 7, 2026
Kate Su of the Space Science Institute in Boulder, Colorado, led a team of astronomers that used Webb to investigate these unusual systems in greater detail.
From Science Daily ● Oct. 7, 2026
And instead of warm days in the summer, Boulder gets more heat waves that lead to “premature deaths” and “adverse economic impacts,” particularly on outdoor labor sectors like agriculture and construction.
From Slate ● Oct. 5, 2026
I lie still, waiting for this mystery monster, whatever made Boulder and Maple disappear.
From "Wayward Creatures" by Dayna Lorentz
He recently won three beautification awards for a Rancho Santa Fe home where he replaced foundation plants with boulders, gravel, cement pots and flameproof steel plant sculptures with internal lighting.
From The Wall Street Journal ● Oct. 21, 2026
Because the returned samples were much smaller than the enormous boulders covering Bennu, scientists needed a way to determine how heat would move through the material on a much larger scale.
From Science Daily ● Oct. 20, 2026
Living shorelines, such as those along the Orange and San Diego county coasts, involve piling sand atop boulders or smaller stones and covering the berms with vegetation.
From Los Angeles Times ● Oct. 17, 2026
Before the building work started, the general was said to have rolled large boulders found at the summit - and ideally suit for construction - downhill.
From BBC ● Oct. 1, 2026
The boulders make a winding path to one giant mesa, a large hill with a flat top.
From "A Rover's Story" by Jasmine Warga
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Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
