humdrum vs mind-numbing

humdrum

adj
  • Lacking variety or excitement; dull; boring. 

noun
  • The quality of lacking variety or excitement. 

mind-numbing

adj
  • Excessively boring, tedious, or dull; repetitive; of an activity, etc., lacking any interest or variety that might serve as intellectual stimulation. 

How often have the words humdrum and mind-numbing occurred in a corpus of books? (source: Google Ngram Viewer )