roughness vs subtlety

roughness

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

  • Abundance, especially of food. 

  • Roughage; coarse fodder. 

  • The property of being rough, coarseness. 

  • Something that is rough; a rough spot. 

subtlety

noun
  • The quality of being done in a clever way that is not obvious or not direct; the quality of being carefully thought out. 

  • The quality of being able to notice or understand things that are not obvious. 

  • An instance of being subtle, a subtle thing, especially a subtle argument or distinction. 

  • The quality of being able to achieve one's aims through clever, delicate or indirect methods. 

  • The quality of being scarcely noticeable or difficult to discern. 

  • An ornate medieval illusion dish or table decoration, especially when made from one thing but crafted to look like another. 

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