Crystal-field excitations and vibronic modes in the triangular-lattice spin-liquid candidate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>TbInO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

We study the ground state properties, electronic excitations and lattice dynamics in spin-liquid candidate TbInO$_3$. By employing polarization resolved Raman spectroscopy we define inter- intra-multiplet excitations, establish low-energy crystal-field (CF) level scheme. In particular, demonstrate that of Tb$^{3+}$ ions is a non-Kramers doublet, relate enhanced linewidth CF modes to magnetic fluctuations near state. identify all 38 allowed Raman-active phonon at low temperature. Moreover, observe hybrid vibronic involving coupled low-lying modes, suggesting strong spin-lattice dynamics. develop model for states obtain parameters bare responses coupling strength. further obtained scheme consistent with specific heat data.