callus vs tunnel

callus

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

  • 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. 

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

verb
  • To form such hardened tissue. 

tunnel

noun
  • A hole in the ground made by an animal, a burrow. 

  • An underground or underwater passage. 

  • A passage through or under some obstacle. 

  • A level passage driven across the measures, or at right angles to veins which it is desired to reach; distinguished from the drift, or gangway, which is led along the vein when reached by the tunnel. 

  • The opening of a chimney for the passage of smoke; a flue. 

  • A wrapper for a protocol that cannot otherwise be used because it is unsupported, blocked, or insecure. 

  • Anything that resembles a tunnel. 

  • A vessel with a broad mouth at one end, a pipe or tube at the other, for conveying liquor, fluids, etc., into casks, bottles, or other vessels; a funnel. 

verb
  • To make a tunnel through or under something; to burrow. 

  • To transmit something through a tunnel (wrapper for insecure or unsupported protocol). 

  • To insert a catheter into a vein to allow long-term use. 

  • To undergo the quantum-mechanical phenomenon where a particle penetrates through a barrier that it classically cannot surmount. 

  • To dig a tunnel. 

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