pullulate vs threefold

pullulate

verb
  • To multiply rapidly. 

  • To teem; to be filled (with). 

  • To germinate. 

threefold

verb
  • To make threefold; to triple. 

adv
  • by a factor of three 

adj
  • triple 

  • three times as great 

noun
  • An algebraic variety of dimension 3. 

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