  Research efforts on the low temperature magnetic order and electronic
properties of U$_3$O$_8$ have been inconclusive so far. Reinterpreting neutron
scattering results, we use group representation theory to show that the ground
state presents collinear out-of-plane magnetic moments, with antiferromagnetic
coupling both in-layer and between layers. Charge localization relieves the
initial geometric frustration, generating a slightly distorted honeycomb
sublattice with N\'eel order. We show, furthermore, that spin-orbit coupling
has a giant effect on the conduction band states and band gap value. Our
results allow a reinterpretation of recent optical absorption measurements.
