The optical conductivity $\sigma (\omega ,T)$ of CeRhSn was studied by broadband infrared spectroscopy. Temperature-dependent spectral weight transfer occurs over high energy ($0.8\mathrm{eV}$) and temperature ($\sim 500\mathrm{K}$) 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 $>10\mathrm{meV}$ 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.

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• Kondo effect
• Optical conductivity
• Heavy-fermion systems
• DFT+DMFT
• Fourier transform infrared spectroscopy