know vs riddle

know

verb
  • To be or become aware or cognizant. 

  • To perceive the truth or factuality of; to be certain of or that. 

  • To experience. 

  • To understand or have a grasp of through experience or study. 

  • To be able to play or perform (a song or other piece of music). 

  • To be acquainted or familiar with; to have encountered. 

  • To be aware of; to be cognizant of. 

  • To recognize as the same (as someone or something previously encountered) after an absence or change. 

  • To have knowledge; to have information, be informed. 

noun
  • Knowledge; the state of knowing. 

  • Knowledge; the state of knowing; now confined to the fixed phrase ‘in the know’ 

riddle

verb
  • To speak ambiguously or enigmatically. 

  • To fill with holes like a riddle. 

  • To fill or spread throughout; to pervade. 

  • To put something through a riddle or sieve; to sieve; to sift. 

  • To solve, answer, or explicate a riddle or question. 

noun
  • A board with a row of pins, set zigzag, between which wire is drawn to straighten it. 

  • A verbal puzzle, mystery, or other problem of an intellectual nature. 

  • A sieve with coarse meshes, usually of wire, for separating coarser materials from finer, as chaff from grain, cinders from ashes, or gravel from sand. 

  • An ancient verbal, poetic, or literary form, in which, rather than a rhyme scheme, there are parallel opposing expressions with a hidden meaning. 

  • One of the pair of curtains enclosing an altar on the north and south. 

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