optical opacity(n = noun.phenomenon) - opacity to light;
is a kind of opacity

opacity, optical, optical aberration, optical activity, optical bench, optical cable, optical condenser, optical crown, optical crown glass, optical device, optical disc, optical disk, optical fiber, optical fibre, optical flint, optical fusion, optical glass, optical illusion, optical instrument, optical lens, optical maser, optical phenomenon, optical prism, optical pyrometer, optical telescope