smouldering vs sullen

smouldering

adj
  • Burning slowly, producing smoke but no flame. 

noun
  • The act by which something smoulders; residual heat. 

sullen

adj
  • Sluggish; slow. 

  • Having a brooding ill temper; sulky. 

  • Gloomy; dismal; foreboding. 

noun
  • Sullen feelings or manners; sulks; moroseness. 

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