earphone vs earplug

earphone

noun
  • A transducer that converts electric signals into sound and is held near the ear, especially as part of a telephone; an earpiece or headphone. 

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. 

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