boulder
noun
a detached and rounded or worn rock, especially a large one.
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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
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
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
The Zunis rained stones down on the invaders; one well-aimed boulder struck Coronado’s helmet.
From The Wall Street Journal ● Apr. 28, 2026
He stopped at a giant boulder beside the trail, where Python lay in the sun.
From "Tristan Strong Punches a Hole in the Sky" by Kwame Mbalia
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
Instead of rain in the spring, Boulder gets more droughts that “have substantial implications for agriculture, wildfires and water availability.”
From Slate ● Oct. 5, 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
Instead of the relatively smooth terrain that earlier observations had suggested, the spacecraft found a rugged landscape dominated by enormous boulders, with very few areas suitable for collecting samples.
From Science Daily ● Oct. 20, 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
He’s still getting to know the boulders, wooden pilings and shards of rusty metal.
From The Wall Street Journal ● Sep. 22, 2026
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
By this time, several archaeologists had joined the expedition and immediately ordered that the powerful naval vessel Mykali be brought back from Athens to aid in the removal of the boulders.
From "Shipwrecked!" by Martin W. Sandler
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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.
