  We present visual-wavelength photometry and spectroscopy of supernova
SN2008S. Based on the low peak luminosity for a SN of M_R = -13.9 mag,
photometric and spectral evolution unlike that of low-luminosity SNe, a
late-time decline rate slower than 56Co decay, and slow outflow speeds of
600-1000 km/s, we conclude that SN2008S is not a true core-collapse SN and is
probably not an electron-capture SN. Instead, we show that SN2008S more closely
resembles a "SN impostor" event like SN1997bs, analogous to the giant eruptions
of LBVs. Its total radiated energy was 1e47.8 ergs, and it may have ejected
0.05-0.2 Msun in the event. We discover an uncanny similarity between the
spectrum of SN 2008S and that of the Galactic hypergiant IRC+10420, which is
dominated by narrow H-alpha, [Ca II], and Ca II emission lines formed in an
opaque wind. We propose a scenario where the vastly super-Eddington wind of
SN2008S partly fails because of reduced opacity due to recombination, as
suggested for IRC+10420. The range of initial masses susceptible to eruptive
LBV-like mass loss was known to extend down to 20-25 Msun, but estimates for
the progenitor of SN2008S (and the similar NGC300 transient) may extend this
range to around 15 Msun. As such, SN2008S may have implications for the
progenitor of SN1987A.
