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.
"It's not a piece of dust, but it's not a meter-size boulder, either."
From Barron's • Apr. 8, 2026
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
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
Evangeline Lilly says she has brain damage after fainting and falling on a boulder at a beach in Hawaii last year.
From Los Angeles Times • Jan. 5, 2026
On the boulder lay Fflewddur’s harp, which played of itself as the wind stirred the strings.
From "The Black Cauldron" by Lloyd Alexander
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.
