instep vs sole

instep

noun
  • The arched part of the top of the foot between the toes and the ankle. 

  • In horses, the hind leg from the ham to the pastern joint. 

  • A section of any footwear covering that part of the foot. 

sole

noun
  • The bottom or plantar surface of the foot. 

  • The end section of the chanter of a set of bagpipes. 

  • A piece of timber attached to the lower part of the rudder, to make it even with the false keel. 

  • The bottom of a furrow. 

  • The bottom of a shoe or boot. 

  • The bottom of the body of a plough; the slade. 

  • The horny substance under a horse's foot, which protects the more tender parts. 

  • The floor inside the cabin of a yacht or boat 

  • Solea solea, a flatfish of the family Soleidae. 

  • The bottom of an embrasure. 

  • The seat or bottom of a mine; applied to horizontal veins or lodes. 

  • A pond or pool; a dirty pond of standing water. 

verb
  • To pull by the ears; to pull about; haul; lug. 

  • to put a sole on (a shoe or boot) 

adj
  • Unique; unsurpassed. 

  • With independent power; unfettered. 

  • Unmarried (especially of a woman); widowed. 

  • Only. 

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