  The spinel FeSc$_2$S$_4$ has been proposed to realize a near-critical
spin-orbital singlet (SOS) state, where entangled spin and orbital moments
fluctuate in a global singlet state on the verge of spin and orbital order.
Here we report powder inelastic neutron scattering measurements that observe
the full bandwidth of magnetic excitations and we find that spin-orbital
triplon excitations of an SOS state can capture well key aspects of the
spectrum in both zero and applied magnetic fields up to 8.5 T. The observed
shift of low-energy spectral weight to higher energies upon increasing applied
field is naturally explained by the entangled spin-orbital character of the
magnetic states, a behavior that is in strong contrast to spin-only singlet
ground state systems, where the spin gap decreases upon increasing applied
field.
