The Collaborative International Dictionary of English v.0.48:

Hobnail \Hob"nail`\, n. [1st hob + nail.]
   1. A short, sharp-pointed, large-headed nail, -- used in
      shoeing houses and for studding the soles of heavy shoes.
      [1913 Webster]

   2. A clownish person; a rustic. --Milton.
      [1913 Webster]

   Hobnail liver (Med.), a disease in which the liver is
      shrunken, hard, and covered with projections like
      hobnails; one of the forms of cirrhosis of the liver.
      [1913 Webster]