  The optical conductivity $\sigma(\omega,T)$ of CeRhSn was studied by
broadband infrared spectroscopy. Temperature-dependent spectral weight transfer
occurs over high energy ($0.8\,$eV) and temperature (${\sim}500\,$K) scales,
classifying CeRhSn as a mixed valent compound. The optical conductivity reveals
a substantial anisotropy in the electronic structure. Renormalization of
$\sigma(\omega,T)$ occurs as a function of temperature to a coherent Kondo
state with concomitant effective mass generation. Associated spectroscopic
signatures were reproduced remarkably well by the combination of density
functional theory and dynamical mean field theory using a momentum-independent
self energy. The theory shows that the anisotropy for energies $>10\,$meV is
mainly driven by the bare three-dimensional electronic structure that is
renormalized by local electronic correlations. The possible influence of
magnetic frustration and quantum criticality is restricted to lower energies.
