We report on a resonant inelastic x-ray scattering study on a single crystal of a nonstoichiometric pyrochlore iridate Tb 2 + x Ir 2 − x O 7 − y ( x ≃ 0.25 ) that magnetically orders at T N ≃ 50 K. We observe a propagating gapped magnon mode at low energy and model it using a Hamiltonian consisting of a Heisenberg exchange [ J = 16.2 ( 9 ) meV ] and Dzyaloshinskii-Moriya interactions [ D = 5.2 ( 3 ) meV ] , which shows the robustness of interactions despite Tb stuffing at the Ir site. Strikingly, the ratio D / J = 0.32 ( 3 ) supports possible nontrivial topological magnon band crossing. This material may thus host coexisting fermionic and bosonic topology, with potential for manipulating electronic and magnonic topological bands thanks to the d − f interaction. Published by the American Physical Society 2024