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boulder

1 American  
[bohl-der] / ˈboʊl dər /
Or bowlder

noun

  1. a detached and rounded or worn rock, especially a large one.

Boulder 2 American  
[bohl-der] / ˈboʊl dər /

noun

  1. a city in N Colorado.

boulder British  
/ ˈbəʊldə /

noun

  1. 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

  2. geology a rock fragment with a diameter greater than 256 mm and thus bigger than a cobble

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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

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

He's perched on a boulder under a warm spring sun.

From BBC • Mar. 13, 2026

Check out the three-foot icicles dripping from the eaves and keep an eye out for the big boulder by the fire station on the right.

From Los Angeles Times • Jan. 29, 2026

One can only imagine the shock and then the exhilaration when it became obvious that the boulder was a huge statue of the divine Greek hero Hercules.

From "Shipwrecked!" by Martin W. Sandler

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.