  We present FEROS--Lick/SDSS, an empirical database of Lick/SDSS spectral
indices of FGK stars to be used in population synthesis projects for
discriminating different stellar populations within the integrated light of
galaxies and globular clusters. From about 2500 FEROS stellar spectra obtained
from the ESO Science Archive Facility we computed line--strength indices for
1085 non--supergiant stars with atmospheric parameter estimates from the AMBRE
project.
  Two samples of 312 {\it dwarfs} and of 83 {\it subgiants} with solar chemical
composition and no significant $\alpha$--element abundance enhancement are used
to compare their observational indices with the predictions of the Lick/SDSS
library of synthetic indices. In general, the synthetic library reproduces very
well the behaviour of observational indices as a function of temperature, but
in the case of low temperature ($T_{\rm eff}$ $\lesssim $5000\,K) dwarfs; low
temperature subgiants are not numerous enough to derive any conclusion. Several
possible causes of the disagreement are discussed and promising theoretical
improvements are presented.
