back out vs callus

back out

verb
  • To draw from behind the back [+accusative = a knife etc.] (as also bare back). 

  • To withdraw from something one has agreed to do. 

  • To exit a mode or function. 

  • To undo (a change). 

  • Coordinate terms: cancel, call off, get cold feet 

  • To reverse (a vehicle) from a confined space. 

  • See also: sell short 

  • To dare (someone) to not withdraw from a challenge. 

  • To bet on someone losing. 

  • Coordinate term: scare off 

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. 

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