Eikonal is the German form of the Greek word εἰκών, meaning likeness, icon or image. It can refer to: Eikonal equation, a non-linear partial differential equation encountered in problems of wave propagation. Eikonal approximation, a method of approximation useful in wave scattering equations. Operation Eikonal, an operation conducted by the National Security Agency in collaboration with the Bundesnachrichtendienst.