boulder vs gravel

boulder

noun
  • A particle greater than 256 mm in diameter, following the Wentworth scale 

  • A large marble, in children's games. 

  • A session of bouldering; involvement in bouldering. 

  • A large mass of stone detached from the surrounding land. 

verb
  • To engage in bouldering. 

gravel

noun
  • A particle from 2 to 64 mm in diameter, following the Wentworth scale. 

  • A type or grade of small rocks, differentiated by mineral type, size range, or other characteristics. 

  • A lameness in the foot of a horse, usually caused by an abscess. 

  • Inability to see at night; night blindness. 

  • gravel cycling, a discipline in cycling different from road cycling, mountain biking or cyclocross, for a large part on gravel roads, typically with a dedicated gravel bike 

  • Small fragments of rock, used for laying on the beds of roads and railways, and as ballast. 

verb
  • To check or stop; to confound; to perplex. 

  • To hurt or lame (a horse) by gravel lodged between the shoe and foot. 

  • To apply a layer of gravel to the surface of a road, etc. 

  • To puzzle or annoy. 

  • To run (as a ship) upon the gravel or beach; to run aground; to cause to stick fast in gravel or sand. 

How often have the words boulder and gravel occurred in a corpus of books? (source: Google Ngram Viewer )