boulder
1 Americannoun
noun
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
- bouldered adjective
- bouldery adjective
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.
As Ryland works to translate Rocky’s language and build a system for the two to communicate, the bond formed between human and pentapedal boulder is palpable.
From Salon • Mar. 21, 2026
He's perched on a boulder under a warm spring sun.
From BBC • Mar. 13, 2026
In her first picture, she stood in a one-piece on a boulder, smiling, a waterfall pummeling behind her.
From Los Angeles Times • Feb. 20, 2026
A 14-year-old girl decorated a large boulder off Greenland’s coast with the letters: “U.S.A. OK.”
From The Wall Street Journal • Jan. 24, 2026
The weight of her gaze is heavier than a boulder.
From "The Manifestor Prophecy" by Angie Thomas
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.
