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:
The Los Angeles neighborhood, which gets its name from a massive boulder in the hills that resembles the face of an eagle, is sandwiched between Pasadena and Glendale and two major freeways.
From Los Angeles Times ● Sep. 9, 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
Having squandered the good-will created by Sam Ryder's success, the BBC delegation now has the tricky task of pushing the boulder back up the hill.
From BBC ● May 17, 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
During the ordeal, Roosevelt had slammed his leg into a boulder, gouging his shin.
From "Death on the River of Doubt" by Samantha Seiple
Oil is vital to the economy and everyday living, and Boulder County hasn’t sought to ban it.
From The Wall Street Journal ● Oct. 6, 2026
Justice Clarence Thomas asked a lawyer representing Boulder.
From The Wall Street Journal ● Oct. 5, 2026
As a result, the complaint says, instead of snow in the winter, Boulder gets more “high-intensity, short-duration rainfall events” that overwhelm its drainage systems and cause flooding.
From Slate ● Oct. 5, 2026
Justice Clarence Thomas asked Russell to identify a “limiting principle” for who could be sued under Boulder County’s legal theory.
From Slate ● Oct. 5, 2026
For Thula, however, Boulder City was about as forlorn a place as could be found on earth.
From "The Boys in the Boat: Nine Americans and Their Epic Quest for Gold at the 1936 Berlin Olympics" by Daniel James Brown
Soon they’d fill with water, and with what writer McPhee called “rock porridge,” a cold rolling lava of mud and debris and boulders the size of Volkswagens.
From Los Angeles Times ● Sep. 17, 2026
"There's boulders bigger than houses - I've never seen that before in my life. It's just an extraordinary operation," the former head of the International Tunnelling Association said.
From BBC ● Aug. 31, 2026
Once rescuers knew where the power stations were, Dix said they could then decide the best way to access them, which typically involves digging and "blasting boulders".
From BBC ● Aug. 31, 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
Below it stretched a long slope of snowy boulders, and beyond that, scarcely a pebble’s throw away, and shimmering in its white winter mantle, lay the Forest.
From "Wolf Brother" by Michelle Paver
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.
