plummet vs somersault

plummet

verb
  • To drop swiftly, in a direct manner; to fall quickly. 

noun
  • A violent or dramatic fall. 

  • A decline; a fall; a drop. 

somersault

verb
  • To perform a somersault. 

noun
  • Starting on one's feet, an instance of rotating one's body 360 degree while airborne or on the ground, with one's feet passing over one's head. 

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