boil vs harden

boil

verb
  • To be agitated like boiling water; to bubble; to effervesce. 

  • To form, or separate, by boiling or evaporation. 

  • To feel uncomfortably hot. 

  • To be moved or excited with passion; to be hot or fervid. 

  • To bring to a boil, to heat so as to cause the contents to boil. 

  • To begin to turn into a gas, seethe. 

  • To heat to the point where it begins to turn into a gas. 

  • To be uncomfortably hot. 

  • To cook in boiling water. 

noun
  • The point at which fluid begins to change to a vapour; the boiling point. 

  • A dish of boiled food, especially seafood. 

  • A social event at which people gather to boil and eat food, especially seafood. (Compare a bake or clambake.) 

  • The collective noun for a group of hawks. 

  • A localized accumulation of pus in the skin, resulting from infection. 

harden

verb
  • To unpalatalize or velarize. 

  • To become or make (a person or thing) resistant or less sensitive. 

  • To become or make (a consonant) more fortis; to (cause to) undergo fortition. 

  • To strengthen. 

  • To make something hard or harder (tough, resistant to pressure). 

  • To modify (a website or other system) to make it resistant to malicious attacks. 

  • To become hard (tough, resistant to pressure). 

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