chinstrap vs surgical mask

chinstrap

noun
  • A strip of leather or material used to fasten a hat or helmet under the chin. 

  • A form of beard that follows the jawline but does not cover the rest of the chin. 

  • A band of colour below a bird's mouth, resembling the chinstrap of a helmet. 

surgical mask

noun
  • A medical-grade mask worn during surgery. 

  • A mask worn to catch bacteria shed in liquid droplets and aerosols from the wearer's mouth and nose. 

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