  LiOsO$_3$ is the first example of a new class of material called a
ferroelectric metal. We performed zero-field and longitudinal-field $\mu$SR,
along with a combination of electronic structure and dipole field calculations,
to determine the magnetic ground state of LiOsO$_3$. We find that the sample
contains both static Li nuclear moments and dynamic Os electronic moments.
Below $\approx 0.7\,$K, the fluctuations of the Os moments slow down, though
remain dynamic down to 0.08$\,$K. We expect this could result in a frozen-out,
disordered ground state at even lower temperatures.
