clingstone vs drupe

clingstone

noun
  • A stone fruit having a stone (pit) that clings to the flesh. 

drupe

noun
  • a kind of fruit, with a fleshy exterior, formed from the exocarp and mesocarp, surrounding a hardened endocarp which protects the seed. 

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