boulder

Synonym discussion

Sense: noun/1

'Boulder' is more specific than both 'rock' and 'stone'. 'Rock' is the widest word and can refer to natural stone of almost any size, from a pebble on the beach to a mountain wall. 'Stone' is also common, but in everyday use it often suggests a smaller piece, or material used in building. A 'boulder' is a single rock so large that people notice it as a separate object in the landscape. 'Pebble' is much smaller, while 'slab' suggests a broad flat shape instead of a heavy rounded mass. So hikers may sit on a boulder beside a river, children throw stones into the pond, and builders cut stone for walls.

Common collocations

Etymology

English boulder seems to come from the older phrase 'boulder stone' in Middle English. That expression was probably influenced by a Scandinavian word related to Swedish dialect bullersten, which meant a large stone in a stream. Later English dropped the second word and kept the shorter form boulder.