emphasise vs underscore

emphasise

underscore

noun
  • An underline; a line drawn or printed beneath text; the character _. 

  • A piece of background music. 

verb
  • To emphasize or draw attention to. 

  • To underline; to mark a line beneath text. 

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