groundnut vs hammerhead

groundnut

noun
  • The nutlike tuber of such a plant, especially peanuts. 

  • A climbing vine, Apios americana, of eastern North America, having fragrant brownish flowers and small edible tubers. 

  • A plant which bears its nutlike seeds underground, such as a peanut (Arachis hypogaea) or a Bambara groundnut (Vigna subterranea). 

  • Any similar plant having underground tubers. 

hammerhead

noun
  • An African fruit bat, the hammer-headed fruit bat, Hypsignathus monstrosus, so called from its large blunt nozzle. 

  • The portion of a hammer containing the metal striking face (also including the claw or peen if so equipped). 

  • A stupid person, a dunce. 

  • A fresh-water fish; the hogsucker, Hypentelium nigricans, in the sucker family Catostomidae. 

  • A kind of ribozyme; hammerhead ribozyme. 

  • Scopus umbretta (hammerkop). 

  • A turn-around; a parking area constructed in a subdivision for initial access and construction. 

  • Any of various sharks of the genera Sphyrna or Zygaena having the eyes set on projections from the sides of the head, which gives it a hammer shape. 

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