  We present X-ray and multi-band optical observations of the afterglow and
host galaxy of GRB 180418A, discovered by ${\it Swift}$/BAT and ${\it
Fermi}$/GBM. We present a reanalysis of the GBM and BAT data deriving durations
of the prompt emission of $T_{90}\approx$2.56s and $\approx$1.90s,
respectively. Modeling the ${\it Fermi}$/GBM catalog of 1405 bursts (2008-2014)
in the Hardness-$T_{90}$ plane, we obtain a probability of $\approx$60% that
GRB 180418A is a short-hard burst. From a combination of ${\it Swift}$/XRT and
${\it Chandra}$ observations, the X-ray afterglow is detected to $\approx$38.5
days after the burst, and exhibits a single power-law decline with $F_{\rm X}
\propto t^{-0.98}$. Late-time Gemini observations reveal a faint
r$\approx$25.69 mag host galaxy at an angular offset of $\approx$0.16''. At the
likely redshift range of z$\approx$1-2.25, we find that the X-ray afterglow
luminosity of GRB 180418A is intermediate between short and long GRBs at all
epochs during which there is contemporaneous data, and that GRB 180418A lies
closer to the $E_{\gamma,{\rm peak}}-E_{\gamma,{\rm iso}}$ correlation for
short GRBs. Modeling the multi-wavelength afterglow with the standard
synchrotron model, we derive the burst explosion properties and find a jet
opening angle of $\theta_{\rm j} \gtrsim 9-14^{\circ}$. If GRB 180418A is a
short GRB that originated from a neutron star merger, it has one of the
brightest and longest-lived afterglows along with an extremely faint host
galaxy. If instead the event is a long GRB that originated from a massive star
collapse, it has among the lowest luminosity afterglows, and lies in a peculiar
space in terms of the Hardness-$T_{90}$ and $E_{\gamma,{\rm
peak}}-E_{\gamma,{\rm iso}}$ planes.
