What does the word Underpinning mean?

Usage examples for Underpinning

  1. And although at first glance his underpinning seemed too frail to bear the great mass of his weight or withstand the effort of his driving power of shoulders and deep, broad thighs, yet a closer reckoning made one aware of the comfortable dimensions of the cannon bone with all that this feature portended. – Bull Hunter by Max Brand
  2. The trouble began at the underpinning. – Partners of the Out-Trail by Harold Bindloss