digester vs heater

digester

noun
  • A strong closed vessel in which bones or other substances may be subjected, usually in water or other liquid, to a temperature above that of boiling, in order to soften them. 

  • One who, or that which, digests. 

heater

noun
  • A device that produces and radiates heat, typically to raise the temperature of a room or building. 

  • A dead heat; a race in which two or more competitors reach the finish line simultaneously. 

  • A medieval European shield having a rounded triangle shape like a clothes iron. 

  • An extended winning streak. 

  • A person who heats something, for example in metalworking. 

  • A fastball, especially one thrown at high velocity. 

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