crucial vs mandatory

crucial

adj
  • Essential or decisive for determining the outcome or future of something; extremely important; vital. 

  • Very good; excellent; particularly applied to reggae music. 

mandatory

adj
  • Obligatory; required or commanded by authority. 

  • Of, being or relating to a mandate. 

noun
  • A sign or line that require the path of the disc to be above, below or to one side of it. 

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