°The space (often triangular) between the outer curve of an arch (the extrados) and a straight-sided figure that bounds it; the space between two contiguous arches and a straight feature above them.
°The triangular space under a stair; the material that fills the space.
°The space (often triangular) between the outer curve of an arch (the extrados) and a straight-sided figure that bounds it; the space between two contiguous arches and a straight feature above them.
°The triangular space under a stair; the material that fills the space.