  We present photometric and spectroscopic follow-up observations of the highly
luminous Type Ibn supernova ASASSN-14ms, which was discovered on UT
2014-12-26.61 at $m_V \sim 16.5$. With a peak absolute $V$-band magnitude
brighter than $-20.5$, a peak bolometric luminosity of $1.7 \times 10^{44}$
ergs s$^{-1}$, and a total radiated energy of $2.1 \times 10^{50}$ ergs,
ASASSN-14ms is one of the most luminous Type Ibn supernovae yet discovered. In
simple models, the most likely power source for this event is a combination of
the radioactive decay of $^{56}$Ni and $^{56}$Co at late times and the
interaction of supernova ejecta with the progenitor's circumstellar medium at
early times, although we cannot rule out the possibility of a magnetar-powered
light curve. The presence of a dense circumstellar medium is indicated by the
intermediate-width He I features in the spectra. The faint ($m_g \sim 21.6$)
host galaxy SDSS J130408.52+521846.4 has an oxygen abundance below
$12+\log(O/H) \lesssim 8.3$, a stellar mass of $M_* \sim 2.6 \times 10^8
M_{\odot}$, and a star formation rate of $\textrm{SFR} \sim 0.02$ $M_{\odot}$
yr$^{-1}$.
