question vs riddle

question

verb
  • To ask a question or questions; inquire or seek to know; examine. 

  • To ask questions of; to interrogate; to ask for information. 

  • To raise doubts about; have doubts about. 

noun
  • A subject or topic for consideration or investigation. 

  • A sentence, phrase or word which asks for information, reply or response; an interrogative. 

  • A proposal to a meeting as a topic for deliberation. 

  • A doubt or challenge about the truth, accuracy, or validity of a matter. 

riddle

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

  • To fill with holes like a riddle. 

  • To speak ambiguously or enigmatically. 

  • To fill or spread throughout; to pervade. 

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

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 question and riddle occurred in a corpus of books? (source: Google Ngram Viewer )