boulder

Meanings

1. 1
   noun

   a large, naturally detached or rounded rock

   A huge boulder blocked the mountain road after the storm.

2. 2
   noun

   geology: a rock fragment more than 256 millimetres across

   The survey classified the 40-centimetre fragment as a boulder rather than a cobble.

From late Middle English bulder, short for bulder ston ("rounded stone, boulder"). Its further origin is uncertain, but it may be Scandinavian and related to Swedish bullersten, a large stream stone around which water roars. Bowlder is a historical spelling.

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