boulder
n. countable B2 Upper Intermediate US //ˈboʊɫdɝ// UK //bˈəʊldɐ// boul·der
n. a very large rock that has been worn smooth by water or weather. You usually find them in nature, like in a river or on a mountain.
n. a large, detached rock mass, typically worn or rounded by the action of water or weather. In geological contexts, it specifically refers to a rock fragment with a diameter greater than 256 millimetres.
The hikers sat on a large boulder to eat their lunch.
Heavy rains caused several boulders to slide down the mountain and block the main highway.
The landscape was dominated by massive granite boulders, smoothed over millennia by glacial movement and the relentless force of the surrounding river.
Usage
Commonly used in the context of climbing, hiking, and geology.