  Group-VI monochalcogenides are attracting a great deal of attention due to
their peculiar anisotropic properties. Very recently, it has been suggested
that GeS could act as a promissory absorbing material with high input-output
ratios, relevant features for designing prospective optoelectronic devices. In
this work, we use the \emph{ab-initio} many body perturbation theory to study
the role of the electron-phonon coupling on orthorhombic GeS. We identify the
vibrational modes that efficiently couple with the electronic states
responsible for giving rise to the first and second excitonic state. We also
study the finite-temperature optical absorption and show that even at $T\to0K$,
the role of the electron-phonon interaction is crucial to properly describe the
main experimental excitation peaks position and width. Our results suggest that
the electron-phonon coupling is essential to properly describe the optical
properties of the monochalcogenides family.
