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
muffle â(third-person singular simple present muffles, present participle muffling, simple past and past participle muffled) ( 1 transitive) To wrap (a person, face etc.) in fabric or another covering, for warmth or protection; often with up.  Addison.