billow vs distend

billow

verb
  • To swell out or bulge. 

  • To surge or roll in billows. 

noun
  • A large wave, swell, surge, or undulating mass of something, such as water, smoke, fabric or sound 

distend

verb
  • To cause to swell. 

  • To extend or expand, as from internal pressure; to swell 

  • To cause gravidity. 

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