smouldering vs sweltering

smouldering

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

adj
  • Burning slowly, producing smoke but no flame. 

sweltering

noun
  • The situation of being or feeling hot and humid. 

adj
  • hot and humid; oppressively sticky 

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