  We present an analysis of a ~160 ks NuSTAR observation of the nearby bright
Seyfert galaxy IC4329A. The high-quality broadband spectrum enables us to
separate the effects of distant reflection from the direct coronal continuum,
and to therefore accurately measure the high-energy cutoff to be
$E_{cut}=178^{+74}_{-40}$ keV. The coronal emission arises from accretion disk
photons Compton up-scattered by a thermal plasma, with the spectral index and
cutoff being due to a combination of the finite plasma temperature and optical
depth. Applying standard Comptonization models, we measure both physical
properties independently using the best signal-to-noise obtained to date in an
AGN over the 3-79 keV band. We derive $kT_e=37^{+7}_{-6}$ keV with
$\tau=1.25^{+0.20}_{-0.10}$ assuming a slab geometry for the plasma, and
$kT_e=33^{+6}_{-6}$ keV with $\tau=3.41^{+0.58}_{-0.38}$ for a spherical
geometry, with both having an equivalent goodness-of-fit.
