threefold vs triadic

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. 

triadic

adj
  • Of or relating to a triad. 

  • Having an arity of three; taking three arguments or operands. 

  • Being or relating to interpreting that involves three parties, i.e. the two clients and the interpreter. 

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