The Collaborative International Dictionary of English v.0.48:

Madrier \Ma*drier"\, n. [F., from Sp. madero, or Pg. madeiro,
   fr. Sp. madera wood for building, timber, Pg. madeira, L.
   materia stuff, materials, lumber. See Matter.]
   A thick plank, used for several mechanical purposes;
   especially:
   (a) A plank to receive the mouth of a petard, with which it
       is applied to anything intended to be broken down.
   (b) A plank or beam used for supporting the earth in mines or
       fortifications.
       [1913 Webster]