Butment

n.
  1. (Arch.) A buttress of an arch; the supporter, or that part which joins it to the upright pier.
  2. (Masonry) The mass of stone or solid work at the end of a bridge, by which the extreme arches are sustained, or by which the end of a bridge without arches is supported.
    3. Butment cheek (Carp.),
    the part of a mortised timber surrounding the mortise, and against which the shoulders of the tenon bear.