boon vs plus sign

boon

noun
  • A good thing; a blessing or benefit; a thing to be thankful for. 

  • The woody portion of flax, separated from the fiber as refuse matter by retting, braking, and scutching. 

  • An unpaid service due by a tenant to his lord. 

adj
  • gay; merry; jovial; convivial. 

plus sign

noun
  • The symbol + used to denote the operation of addition, to indicate that a number is positive, and so on. 

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