  We present the calibration of the spectroscopic Lick/IDS standard line-index
system for measurements obtained with the Gemini Multi-Object Spectrographs
known as GMOS-North and GMOS- South. We provide linear correction functions for
each of the 25 standard Lick line indices for the B600 grism and two
instrumental setups, one with 0.5 arcsecond slit width and 1x1 CCD pixel
binning (corresponding to ~2.5 Angstroem spectral resolution) and the other
with 0.75 arcsecond slit width and 2x2 binning (~4 Angstroem). We find small
and well-defined correction terms for the set of Balmer indices Hbeta, HgammaA,
and HdeltaA along with the metallicity sensitive indices Fe5015, Fe5270,
Fe5335, Fe5406, Mg2 and Mgb that are widely used for stellar population
diagnostics of distant stellar systems. We find other indices that sample
molecular absorption bands, such as TiO1 and TiO2, with very wide wavelength
coverage or indices that sample very weak molecular and atomic absorption
features, such as Mg1, as well as indices with particularly narrow passband
definitions, such as Fe4384, Ca4455, Fe4531, Ca4227, and Fe5782, less robustly
calibrated. These indices should be used with caution.
