trepan vs trephine

trepan

noun
  • A surgical instrument used to remove a circular section of bone from the skull; a trephine. 

  • A tool used to bore through rock when sinking shafts. 

verb
  • To create a large hole by making a narrow groove outlining the shape of the hole and then removing the plug of material remaining by less expensive means. 

  • To use a trepan; to trephine. 

trephine

noun
  • A surgical instrument with a cylindrical blade used to remove a circular section of tissue, f.e. bone or cornea; a trepan. 

verb
  • To use a trephine during surgery. 

  • To perforate with a trephine. 

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