crossword vs crux

crossword

noun
  • The grid of such a puzzle 

  • A word puzzle in which interlocking words are entered usually horizontally and vertically into a grid based on clues given for each word. 

crux

noun
  • A puzzle or difficulty. 

  • The basic, central, or essential point or feature. 

  • The critical or transitional moment or issue, a turning point. 

  • The hardest point of a climb. 

  • A cross on a coat of arms. 

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