Thermomagnetic and inelastic neutron-scattering measurements on ${\mathrm{Na}}_2\mathrm{Pr}{\mathrm{O}}_3$ are reported. This material is an antiferromagnetic honeycomb magnet based on the tetravalent lanthanide ${\mathrm{Pr}}^{4+}$ and has been proposed to host dominant antiferromagnetic Kitaev interactions. These measurements reveal magnetic fluctuations in ${\mathrm{Na}}_2\mathrm{Pr}{\mathrm{O}}_3$ below an energy of 2 meV as well as crystal-field excitations around 230 meV. The latter energy is comparable to the scale of the spin-orbit interaction and explains both the very small effective moment of around $1.0{\mu }_{\mathrm{B}}$ per ${\mathrm{Pr}}^{4+}$ and the difficulty to uncover any static magnetic scattering below the ordering transition at $T_{\mathrm{N}}=$ 4.6 K. By comparing the low-energy magnetic excitations in ${\mathrm{Na}}_2\mathrm{Pr}{\mathrm{O}}_3$ to those of the isostructural spin-only compound, ${\mathrm{Na}}_2\mathrm{Tb}{\mathrm{O}}_3$, a microscopic model of exchange interactions is developed that implicates dominant and surprisingly large Heisenberg exchange interactions $J\approx 1.1\left(1\right)$ meV. Although antiferromagnetic Kitaev interactions with $\mathit{\text{K}}\le 0.2J$ cannot be excluded, the inelastic neutron-scattering data of ${\mathrm{Na}}_2\mathrm{Pr}{\mathrm{O}}_3$ is best explained with a $\mathrm{\Delta }=1.22$ easy-axis XXZ exchange anisotropy.

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• Spin dynamics
• Lanthanides
• Crystal-field theory
• Kitaev-Heisenberg model