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:
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
"It's not a piece of dust, but it's not a meter-size boulder, either."
From Barron's ● Apr. 8, 2026
“No cause for alarm, Brother Alf. Ambrose Spike is made of leather and needles. Tough as a boulder, this old ruffian is. Look, he’s beginning to come around already.”
From "Redwall" by Brian Jacques
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
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
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
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
Whatever took Maple and Boulder after they ate the human food, it’s here.
From "Wayward Creatures" by Dayna Lorentz
In another dry sauna, they heat boulders overnight so they emit heat continuously.
From Los Angeles Times ● Oct. 27, 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
That was the case with hydraulic mining in the West, which involved aiming a torrent of water under high pressure to blast away soil and boulders to expose the underlying gold veins.
From Los Angeles Times ● Oct. 13, 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
At the Hissing Stones, she had to leave the wagon and carry everything over the black boulders to the cave.
From "Nim’s Island" by Wendy Orr
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Get a wordDefinitions 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.
