auditor vs headphone

auditor

noun
  • One who listens, typically as a member of an audience. 

  • One who audits an academic course; who attends the lectures but does not earn academic credit. 

  • One trained to perform spiritual guidance procedures. 

  • In many jurisdictions, an elected or appointed public official in charge of the public accounts; a comptroller. 

  • One who audits bookkeeping accounts. 

headphone

noun
  • A cushioned speaker placed on, over, or inside the ear, normally used in left/right pairs. 

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