Newtonian UK /njuːˈtəʊ.ni.ən/US /n(j)uˈtoʊ.ni.ən/adjective 4noun 2forms 3 adjective4 •Of or relating to Isaac Newton, or his laws and theories. •Of or relating to classical physics that does not take relativity into account. •Obeying Newton's law of viscosity; i.e. having a constant viscosity. •Being or relating to a type of reflecting telescope using a concave primary mirror and a flat diagonal secondary mirror. noun2 •A type of reflecting telescope using a concave primary mirror and a flat diagonal secondary mirror. •A scientist supporting Isaac Newton's views on physics and mathematics. formsNewtonians · more Newtonian · most Newtonian