doormat vs house slipper

doormat

noun
  • A coarse mat at the entrance to a house, upon which one wipes one's shoes. 

  • Someone who is overly submissive to others' wishes. 

house slipper

noun
  • A slipper designed to be worn inside the house 

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