  We present results from light scattering experiments on tetragonal FeS with
the focus placed on lattice dynamics. We identify the Raman active A1g and B1g
phonon modes, a second order scattering process involving two acoustic phonons,
and contributions from potentially defect-induced scattering. The temperature
dependence between 300 and 20K of all observed phonon energies is governed by
the lattice contraction. Below 20K the phonon energies increase by 0.5-1
cm$^{-1}$ thus indicating putative short range magnetic order. Along with the
experiments we performed lattice-dynamical simulations and a symmetry analysis
for the phonons and potential overtones and find good agreement with the
experiments. In particular, we argue that the two-phonon excitation observed in
a gap between the optical branches becomes observable due to significant
electron-phonon interaction.
