callus vs etch

callus

verb
  • To form such hardened tissue. 

noun
  • A shining area on the frons of many species of Tabanomorpha (horse flies and relatives). 

  • The material of repair in fractures of bone; a substance exuded at the site of fracture, which is at first soft or cartilaginous in consistency, but is ultimately converted into true bone and unites the fragments into a single piece. 

  • The new formation over the end of a cutting, before it puts out rootlets. 

  • A hardened area of the skin (especially on the foot or hand) caused by repeated friction, wear or use. 

etch

verb
  • To engrave a surface. 

  • To make a lasting impression. 

  • To cut into a surface with an acid or other corrosive substance in order to make a pattern. Best known as a technique for creating printing plates, but also used for decoration on metal, and, in modern industry, to make circuit boards. 

  • To sketch; to delineate. 

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