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:
Olympic rock climbing champion Toby Roberts - who won gold in the boulder and lead event at Paris 2024 - was also made an MBE on Tuesday.
From BBC ● May 5, 2026
"It's not a piece of dust, but it's not a meter-size boulder, either."
From Barron's ● Apr. 8, 2026
Like any sensible American trying to move a boulder up a hill, he has lawyers on call.
From The Wall Street Journal ● Feb. 6, 2026
Using this information, the AI identified important surface features such as bedrock, outcrops, boulder fields, and sand ripples.
From Science Daily ● Jan. 31, 2026
In the lee of a boulder, a circle of sphinxes was eating something meaty and unidentifiable, tearing at it with teeth as long as his fingers and twice as thick.
From "Impossible Creatures" by Katherine Rundell
The latest discovery came Sunday at Boulder Beach on the western part of the Lake Mead National Recreation Area in Nevada, according to national park officials.
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 University of Arizona in Tucson operates the HiRISE camera, which was built by BAE Systems in Boulder, Colorado.
From Science Daily ● Jul. 14, 2026
The 18-year-old has been accepted to University of Colorado Boulder but deferred for a year.
From BBC ● Jul. 4, 2026
He went over Bradbury’s head to Gordon Dean to propose instead an independent new lab in Boulder, Colorado, where some 130 physicists would report to him alone.
From "Big Science" by Michael Hiltzik
Shannon, 11, was on a school residential trip on Dartmoor in Devon when her leg got trapped between enormous granite boulders on Hound Tor on Tuesday.
From BBC ● Jun. 27, 2026
With parting the sea for “The Ten Commandments” and then the boulders coming down the hill during the rockslide?
From Los Angeles Times ● May 29, 2026
Stream engineering aims to improve habitats and water flow, for example by building dams or placing boulders in a stream, and these efforts have cost hundreds of millions of dollars over the years.
From Slate ● Apr. 28, 2026
Somehow, creaky tiled houses have been wedged here between enormous outcroppings of glacial boulders.
From The Wall Street Journal ● Mar. 27, 2026
Percy scanned the cliffs and boulders, alert for more monsters, but nothing else appeared.
From "The House of Hades" by Rick Riordan
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.
