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.
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Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Meng has responded to criticism of this vote, noting that thanking ICE was not the only provision in the resolution, which condemned the attack on Jewish community members in Boulder, Colorado, on June 1, 2025.
From Salon • Jun. 4, 2026
Ochwat and study co author Ted Scambos, a senior research scientist at the University of Colorado Boulder, said new satellite technologies could significantly improve scientists' understanding of rapid glacier retreat.
From Science Daily • May 19, 2026
"Our mother suffered indescribable pain for more than three weeks before succumbing to her injuries," said the statement read by Boulder County District Attorney Michael Dougherty, according to the Denver Post.
From Barron's • May 7, 2026
Dan Caruso, a tech investor who founded the Boulder, Colo.-headquartered bandwidth provider Zayo, collected hundreds of signatures for an open letter he sent to state leaders with a list of deregulatory demands.
From The Wall Street Journal • May 4, 2026
Whatever took Maple and Boulder after they ate the human food, it’s here.
From "Wayward Creatures" by Dayna Lorentz
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.
