felt-tip vs permanent marker

felt-tip

noun

  • A felt-tip pen. 

verb

  • To write with a felt-tip pen. 

permanent marker

noun

  • a type of felt-tip pen used to create permanent water-resistant writing on a surface such as a writable DVD 

How often have the words felt-tip and permanent marker occurred in a corpus of books? (source: Google Ngram Viewer )