  We report the serendipitous discovery of Gaia17bpp/2MASS J19372316+1759029, a
star with a deep single large-amplitude dimming event of $\sim$4.5 magnitudes
that lasted over 6.5 years. Using the optical to IR spectral energy
distribution (SED), we constrain the primary star to be a cool giant M0-III
star with effective temperature $T_{\text{eff}}$=3,850 K and radius R=58
R$_{\odot}$. Based on the SED fitting, we obtained a bimodal posterior
distribution of primary stellar masses at 1.5 M${\odot}$ and 3.7 M${\odot}$.
Within the last 66 years of photometric coverage, no other significant dimming
events of this depth and duration were identified in the optical light curves.
Using a Gaussian Process, we fit a high-order Gaussian model to the optical and
IR light curves and conclude the dimming event exhibits moderate asymmetries
from optical to IR. At the minimum of the dimming event, the (W$_{1}$-W$_{2}$)
color was bluer by $\sim$0.2 mag relative to the primary star outside the
dimming event. The ingress and egress colors show a shallow reddening profile.
We suggest that the main culprit of the dimming event is likely due to the
presence of a large, optically thick disk transiting the primary giant star. By
fitting a monochromatic transit model of an oblate disk transiting a star, we
found good agreement with a slow-moving, 0.005 km sec$^{-1}$, disk with a
$\sim$1.4 AU radius. We propose that Gaia17bpp belongs to a rare binary star
population similar to the Epsilon Aurigae system, which consists of a secondary
star enshrouded by an optically thick debris disk.
