dry rot vs must

dry rot

noun
  • Any progression of decay, corruption, or obsolescence. 

  • The crumbly, friable decayed portions of wooden members of buildings, especially at or below grade, usually caused by a fungal infection. 

  • A fungal infection which affects plants, in particular potatoes. 

must

noun
  • The property of being stale or musty. 

  • Something that exhibits the property of being stale or musty. 

  • Fruit juice that will ferment or has fermented, usually from grapes. 

  • Something that is mandatory or required. 

verb
  • To do as a requirement; indicates that the sentence subject is required as an imperative or directive to execute the sentence predicate, with failure to do so resulting in a failure or negative consequence. 

  • To become musty. 

  • Used to indicate that something that is very likely, probable, or certain to be true. 

  • To do with certainty; indicates that the speaker is certain that the subject will have executed the predicate. 

  • To make musty. 

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