earthnut vs groundnut

earthnut

noun
  • Synonym of peanut (Arachis hypogaea) 

  • The underground tuber belonging to the genus Tuber; the truffle. 

  • The dwarf ginseng: Panax trifolius 

  • A tuber belonging to the species Conopodium majus (syns. Bunium flexuosum, Conopodium denudatum), Bunium bulbocastanum (syn. Carum bulbocastanum), or Apios americana (syn. Apios tuberosa) 

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. 

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