slowness vs somnolence

slowness

noun
  • The quality or state of being slow. 

  • A unit, the reciprocal of velocity, that delineates the amount of time required for an object to travel a given distance. 

somnolence

noun
  • A state of drowsiness or sleepiness. 

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