The energies of the frustrated translational vibrations parallel to the surface (T-mode) of isolated CO molecules adsorbed on various flat, regularly stepped and defective surfaces of copper have been measured using high resolution He-atom scattering. Whereas on the Cu(111) and Cu(001) surfaces CO has a T-mode energy of about 4.0 meV, at the steps of the Cu(211) and Cu(511) surfaces it is reduced to 3.0 meV. The same energy was observed for scattering parallel and perpendicular to the step edge directions. At defects, which were created by sputtering under different conditions, two additional T-mode energies of 3.2 meV and 2.5 meV were observed and are attributed to CO molecules adsorbed at step edges and at "isolated" defects, respectively.