once vs threefold

once

conj
  • As soon as; when; after. 

adv
  • Multiplied by one: indicating that a number is multiplied by one. 

  • One and only one time. 

  • Formerly; during some period in the past. 

threefold

adj
  • triple 

  • three times as great 

verb
  • To make threefold; to triple. 

adv
  • by a factor of three 

noun
  • An algebraic variety of dimension 3. 

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