  We used near-infrared spectroscopy at medium-high resolution
(R=8,000$-$25,000) to perform the first comprehensive chemical study of the
intermediate luminosity bulge globular cluster Terzan~6. We derived detailed
abundances and abundance patterns of 27 giant stars, likely members of
Terzan~6, based on their accurate Hubble Space Telescope proper motions and
line-of-sight radial velocities. From the spectral analysis of these stars, we
determined an average heliocentric radial velocity of 143.3$\pm$1.0 km s$^{-1}$
with a velocity dispersion of 5.1$\pm$0.7 km s$^{-1}$ and an average
[Fe/H]=$-0.65\pm0.01$ and a low 1$\sigma$ dispersion of 0.03 dex. We also
measured some depletion of [Mn/Fe] with respect to the solar-scaled values and
enhancement of for [Ca/Fe], [Si/Fe], [Mg/Fe], [Ti/Fe], [O/Fe], [Al/Fe],
[Na/Fe], and, to a lower extent, for [K/Fe], consistent with previous
measurements of other bulge globular clusters and favoring the scenario of a
rapid bulge formation and chemical enrichment. Some spread in the light element
abundances suggest the presence of first- and second-generation stars, typical
of genuine globulars. Finally, we measured some depletion of carbon and low
$\rm ^{12}C/^{13}C$ isotopic ratios, as in previous studies of field and
cluster bulge giants, indicating that extra-mixing mechanisms should be at work
during the post main sequence evolution in the high metallicity regime as well.
