earplug vs listener

earplug

noun
  • A piece of protective gear meant to be inserted in the ear canal to protect the wearer's hearing from loud noises or the intrusion of water. 

verb
  • To fit with earplugs. 

listener

noun
  • A person's ear. 

  • Someone who listens, especially to a speech or a broadcast. 

  • A musical anthology. 

  • A function that runs in response to an event; an event handler. 

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