  The absolute atomic mass of $^{208}$Pb has been determined with a fractional
uncertainty of $7\times 10^{-11}$ by measuring the cyclotron-frequency ratio
$R$ of $^{208}$Pb$^{41+}$ to $^{132}$Xe$^{26+}$ with the high-precision
Penning-trap mass spectrometer Pentatrap and computing the binding energies
$E_{\text{Pb}}$ and $E_{\text{Xe}}$ of the missing 41 and 26 atomic electrons,
respectively, with the ab initio fully relativistic multi-configuration
Dirac-Hartree-Fock (MCDHF) method. $R$ has been measured with a relative
precision of $9\times 10^{-12}$. $E_{\text{Pb}}$ and $E_{\text{Xe}}$ have been
computed with an uncertainty of 9.1 eV and 2.1 eV, respectively, yielding
$207.976\,650\,571(14)$ u (u$=9.314\,941\,024\,2(28)\times 10^{8}$ eV/c$^2$)
for the $^{208}$Pb neutral atomic mass. This result agrees within $1.2\sigma$
with that from the Atomic-Mass Evaluation (AME) 2020, while improving the
precision by almost two orders of magnitude. The new mass value directly
improves the mass precision of 14 nuclides in the region of Z=81-84 and is the
most precise mass value with A>200. Thus, the measurement establishes a new
region of reference mass values which can be used e.g. for precision mass
determination of transuranium nuclides, including the superheavies.
