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
Full Definition of MULLION. : a slender vertical member that forms a division between units of a window, door, or screen or is used decoratively. â mullion transitive verb.See mullion defined for English-language learners.See mullion defined for kids. ADVERTISEMENT. an upright piece of wood, stone, metal, etc., that separates two windows.