coverall vs overalls

coverall

noun
  • A loose-fitting protective garment worn over other clothing. 

overalls

noun
  • A loose-fitting garment worn over regular clothes to protect them. 

  • Trousers traditionally worn by cavalry. 

  • Loose-fitting pants with supporting cross-straps and a panel of material in the chest (called a bib), often associated with farm work. 

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