The synergistic interplay between spin correlations, spin-orbit coupling, and competing exchange interactions provides a promising route to realize exotic quantum states with nontrivial excitations in rare-earth-based frustrated magnets. Here, by using thermodynamic and local-probe measurements down to 16 mK, we demonstrate the exotic magnetism and spin dynamics in the distorted triangular lattice ${\mathrm{TbBO}}_3$. Thermodynamic experiments reveal the presence of dominant antiferromagnetic exchange and subdominant dipolar interactions. Despite sizable antiferromagnetic exchange interactions between the ${\mathrm{Tb}}^{3+}$ moments, the muon-spin relaxation experiment do not detect any signatures of long-range magnetic order or spin-freezing down to 16 mK, corroborating the specific heat and $ac$ magnetic susceptibility data down to 45 mK that suggests a persistent spin dynamics in this frustrated triangular lattice. The scaling of muon relaxation rate as a function of the characteristic energy scale for several spin-liquid candidates, including ${\mathrm{TbBO}}_3$, demonstrates that a common underlying mechanism is at play. The persistent dynamics in this frustrated triangular lattice antiferromagnet is reminiscent of a universal spin-liquid-like spin fluctuations, here attributed to dominant two dimensional (2D) antiferromagnetic short-range spin correlations, confirmed by the presence of a broad magnetic diffuse scattering in the elastic and low-energy inelastic neutron scattering channels at $Q\approx 1.03 {\text{Å}}^{-1}$ at low temperatures. Our results demonstrate that non-Kramers ion based triangular lattice hosts spin-liquid-like dynamics of local moments arising from the admixture of excited crystal electric field states into the ground state and intertwining of frustration and spin-orbit interaction.

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• Continuum mechanics
• Crystal-field excitations
• Frustrated magnetism
• Magnetic susceptibility
• Magnetism
• Quantum spin liquid
• Specific heat
• Antiferromagnets
• Honeycomb lattice
• Density functional theory
• Magnetization measurements
• Muon spin relaxation & rotation
• Nuclear magnetic resonance
• Specific heat measurements
• Susceptibility measurements