boulder

/ˈbəʊl.də(ɹ)/noun

A very big rock that sits apart from the ground around it.

Example sentence

“A huge boulder blocked the hiking trail after the storm.”

The top of the size scale: pebble, stone, rock, boulder. Climbers turned it into the sport of "bouldering", done low without ropes.

Related words

gravelSmall loose pieces of stone, often spread on paths, roads, and railway beds.cavernA cave of great size.sandTiny loose grains of worn-down rock, finer than gravel, found on beaches and in deserts and used in building.caveA big natural hollow space underground or in the side of a cliff or hill.duneA mound or ridge of sand built up by the wind or by moving water.slopeA stretch of ground that rises or falls at a steady angle.