The Collaborative International Dictionary of English v.0.48:

pitprop \pit"prop\ n.
   A wooden prop used to support the roof of a mine temporarily.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

pitprop \pit"prop\ n.
   A wooden prop used to support the roof of a mine temporarily.
   [WordNet 1.5] pits

WordNet (r) 3.0 (2006):

pitprop
    n 1: a wooden prop used to support the roof of a mine [syn:
         pitprop, sprag]