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abstract: 'UM 625, previously identified as a narrow-line active galactic nucleus (AGN), actually exhibits broad [H$\alpha$]{} and [H$\beta$]{} lines whose width and luminosity indicate a low black hole mass of $1.6 \times 10^6$ [$M_{\odot}$]{}. We present a detailed multiwavelength study of the nuclear and host galaxy properties of UM 625. Analysis of [*Chandra*]{} and [*XMM-Newton*]{} observations suggests that this system contains a heavily absorbed and intrinsically X-ray weak (${\ensuremath{\alpha_{\rm{ox}}}}=-1.72$) nucleus. Although not strong enough to qualify as radio-loud, UM 625 does belong to a minority of low-mass AGNs detected in the radio. The broad-band spectral energy distribution constrains the bolometric luminosity to ${\ensuremath{L\mathrm{_{bol}}}}\approx(0.5-3)\times10^{43}$ [erg s$^{-1}$]{} and ${{\ensuremath{L\mathrm{_{bol}}}}/{\ensuremath{L\mathrm{_{Edd}}}}}\approx0.02-0.15$. A comprehensive analysis of Sloan Digital Sky Survey and [*Hubble Space Telescope*]{} images shows that UM 625 is a nearly face-on S0 galaxy with a prominent, relatively blue pseudobulge ([Sérsic]{} index $n = 1.60$) that accounts for $\sim$60% of the total light in the $R$ band. The extended disk is featureless, but the central $\sim150-400$ pc contains a conspicuous semi-ring of bright, blue star-forming knots, whose integrated ultraviolet luminosity suggests a star formation rate of $\sim$0.3 [$M_{\odot}$]{} yr$^{-1}$. The mass of the central black hole roughly agrees with the value predicted from 