undershoe

under- +‎ shoe

undershoe (plural undershoes)

1. A covering for the foot, sturdier than a sock, worn under the outer shoes.
   • 1900, Official Gazette of the United States Patent Office, page 2576:

     The rubber overshoe is made to protect only the ball of the foot or is provided with an opening through which the heel of the undershoe projects.

   • 1973, Dennis Rawlins, Peary at the North Pole: Fact Or Fiction?, page 43:

     Then he inserted the blade of his knife under the top of Peary's sealskin boots. He ripped the boots from both feet and gently removed the rabbitskin undershoes.