pellet vs spherule

pellet

noun
  • A small, compressed, hard chunk of matter. 

  • One of the short conductive tubes in a Pelletron particle accelerator. 

  • A lead projectile used as ammunition in rifled air guns. 

  • Compressed byproduct of digestion regurgitated by owls and many other birds of prey, which serves as a waste disposal mechanism for indigestible parts of food, such as fur and bones. 

  • A roundel sable (black circular spot). 

verb
  • To form into pellets. 

  • To strike with pellets. 

spherule

noun
  • A small sphere. 

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