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
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
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.
Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!
Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!
Want to remember this word for good? Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we'll help you make the most of your study time!
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
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
City crews placed a boulder over the manhole cover, a spokesperson who was at the scene Wednesday said but, by the following morning, the boulder had been moved.
From Los Angeles Times ● Mar. 25, 2026
At the bottom of a boulder she found the first victim.
From "A Girl Named Disaster" by Nancy Farmer
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
Co-author Dr David Wilson, research associate at the University of Colorado Boulder, explained their findings revealed some unusual activity.
From BBC ● Jul. 14, 2026
More broadly, recent research External link from the University of Colorado Boulder finds that after an ICE surge, employment among remaining immigrants declines 4% on average.
From Barron's ● Jun. 25, 2026
But Boulder could determine whether accountability arrives first.
From Slate ● Jun. 25, 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
Early in his career Noguchi was identified as a sculptor, known for modernist abstractions—enigmas in wood, stone, metals, plaster, ceramic and aluminum—that conjure totems, boulders, edifices and artifacts, while synthesizing Western and Eastern traditions.
From The Wall Street Journal ● Jul. 1, 2026
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
Photos and a video Aiello provided show bladed wire snaking around the decomposing animal’s neck and curved horns, as well as the front legs, in a desert landscape dotted with boulders.
From Los Angeles Times ● Jun. 3, 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
We were in a draw with boulders on both sides of the trail.
From "Black Star, Bright Dawn" by Scott O'Dell
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.
