Other forms: boulders
A boulder is a rock so huge you could not hope to move it. Bigger than a stone, bigger than a person, sometimes bigger than a car.
Geologists have a size definition, since a boulder is anything over about twenty-five centimetres, though everyday use reserves the word for something genuinely large. Many British boulders were carried and dropped by glaciers, and an erratic is one left far from the rock it came from. Bouldering is climbing on them without ropes, close to the ground.
1nounboulderA very large rock.
“A boulder had come down onto the road overnight.”
A boulder may be a noisy stone. Middle English had bulder ston for a rock worn round, possibly from an Old Swedish word joining bulder, a rumble, to sten, stone: the sound of one shifting in a river.
Middle English
bulder
English, today
boulder
Built from
From late Middle English bulder, short for Middle English bulder ston (“a stone that's been worn into a round shape, boulder, cobblestone”), possibly from gmq-osw buldersten, itself possibly from gmq-osw bulder (“rumble, noise”) + sten (“stone”); whence dialectal Swedish bullersten (“large stone in a stream, causing water to roar around it”). The first element may alternatively be allied to gmq-osw bulle, bolle (“round drinking vessel, tumbler”), from Old Norse bolli, related to Old English bolla (“round object, bowl”), see English bowl.
Etymology from Wiktionary, CC BY-SA