damson vs plum tree

damson

noun

  • The edible fruit of this tree. 

  • A subspecies of plum tree, Prunus domestica subsp. insititia, native to Eurasia. 

adj

  • The color of the fruit of this tree, a very deep purple. 

plum tree

noun

  • A tree that bears plums. 

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