boulder

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 Old Swedish *buldersten, itself possibly from Old Swedish 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 Old Swedish bulle, bolle (“round drinking vessel, tumbler”), from Old Norse bolli, related to Old English bolla (“round object, bowl”), see English bowl.