The Collaborative International Dictionary of English v.0.48:

Flanch \Flanch\, n.; pl. Flanches. [Prov. E., a projection,
   OF. flanche flank. See Flank.]
   1. A flange. [R.]. (Her.) A bearing consisting of a segment
      of a circle encroaching on the field from the side.
      [1913 Webster]

   Note: Flanches are always in pairs. A pair of flanches is
         considered one of the subordinaries.
         [1913 Webster]