  We present a multiwavelength study of the black hole X-ray binary V404 Cyg in
quiescence, focusing upon the spectral energy distribution (SED). Radio,
optical, UV, and X-ray coverage is simultaneous. We supplement the SED with
additional non-simultaneous data in the optical through infrared where
necessary. The compiled SED is the most complete available for this, the X-ray
and radio brightest quiescent black hole system. We find no need for a
substantial contribution from accretion light from the near-UV to the near-IR,
and in particular the weak UV emission constrains published spectral models for
V404 Cyg. We confirm that no plausible companion spectrum and interstellar
extinction can fully explain the mid-IR, however, and an IR excess from a jet
or cool disc appears to be required. The X-ray spectrum is consistent with a
Gamma~2 power-law as found by all other studies to date. There is no evidence
for any variation in the hardness over a range of a factor of 10 in luminosity.
The radio flux is consistent with a flat spectrum (in f(nu)). The break
frequency between a flat and optically thin spectrum most likely occurs in the
mid or far-IR, but is not strongly constrained by these data. We find the radio
to be substantially variable but with no clear correlation with X-ray
variability.
