dullness vs sluggishness

dullness

noun
  • The quality of being slow of understanding things; stupidity. 

  • The quality of not perceiving or kenning things distinctly. 

  • The quality of being uninteresting; boring; humorless or irksome. 

  • Lack of interest or excitement. 

  • The lack of visual brilliance; want of sheen. 

  • bluntness. 

sluggishness

noun
  • The property of being sluggish, unable or unwilling to act quickly. 

  • The state of economic decline, inactivity, slow or subnormal growth. 

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