difficulty vs roughness

difficulty

noun
  • An awkward situation or quarrel. 

  • Physical danger from the environment, especially with risk of drowning 

  • An obstacle that hinders achievement of a goal. 

  • The state of being difficult, or hard to do. 

  • An objection. 

  • That which cannot be easily understood or believed. 

roughness

noun
  • Something that is rough; a rough spot. 

  • A measure of how rough something is, such as a surface 

  • Abundance, especially of food. 

  • Roughage; coarse fodder. 

  • The property of being rough, coarseness. 

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