pit prop

pit prop (plural pit props)

1. A wooden beam used as a support within a mineshaft or tunnel.
   • 1915 December 2, D. Thomas Curtin, “Sweden's Rôle in the Great War”, in The World's Work‎, volume XXXI:

     Whereas Germany at the outbreak of war was the greatest purchaser of Swedish iron ore, Great Britain was by far the greatest buyer of Swedish wood products. German submarines, however, have taken deadly toll of Scandinavian ships laden with pit-props bound for England.

• mine prop