threefold vs twofold

threefold

adj
  • triple 

  • three times as great 

adv
  • by a factor of three 

noun
  • An algebraic variety of dimension 3. 

verb
  • To make threefold; to triple. 

twofold

adj
  • Double; duplicate; multiplied by two. 

  • Having two parts, especially two different parts. 

adv
  • In a double degree; doubly. 

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