When a geometry is described by a set of axioms, the notion of a line is usually left undefined (a so-called primitive object). The properties of lines are then determined by the axioms which refer to them.
Definition of mull 1: friable forest humus that forms a layer of mixed organic matter and mineral soil and merges gradually into the mineral soil beneath 2: a finely powdered solid especially in a suspension
Freebase(0.00 / 0 votes)Rate this definition: Rill. In geomorphology, a rill is a natural fluvial topographic feature. Rills form as the initial signs of erosion as shallow waterways on an exposed slope. Artificial rills are constructed as channels to carry a water supply from a water source some distance away.