  We present a stellar dynamical mass measurement of a newly detected
supermassive black hole (SMBH) at the center of the fast-rotating, massive
elliptical galaxy NGC 2693 as part of the MASSIVE survey. We combine high
signal-to-noise integral field spectroscopy (IFS) from the Gemini Multi-Object
Spectrograph (GMOS) with wide-field data from the Mitchell Spectrograph at
McDonald Observatory to extract and model stellar kinematics of NGC 2693 from
the central $\sim 150$ pc out to $\sim2.5$ effective radii. Observations from
Hubble Space Telescope (HST) WFC3 are used to determine the stellar light
distribution. We perform fully triaxial Schwarzschild orbit modeling using the
latest TriOS code and a Bayesian search in 6-D galaxy model parameter space to
determine NGC 2693's SMBH mass ($M_\text{BH}$), stellar mass-to-light ratio,
dark matter content, and intrinsic shape. We find $M_\text{BH} = \left(1.7\pm
0.4\right)\times 10^{9}\ M_\odot$ and a triaxial intrinsic shape with axis
ratios $p=b/a=0.902 \pm 0.009$ and $q=c/a=0.721^{+0.011}_{-0.010}$, triaxiality
parameter $T = 0.39 \pm 0.04$. In comparison, the best-fit orbit model in the
axisymmetric limit and (cylindrical) Jeans anisotropic model of NGC 2693 prefer
$M_\text{BH} = \left(2.4\pm 0.6\right)\times 10^{9}\ M_\odot$ and $M_\text{BH}
= \left(2.9\pm 0.3\right)\times 10^{9}\ M_\odot$, respectively. Neither model
can account for the non-axisymmetric stellar velocity features present in the
IFS data.
