  A very fundamental and unconventional characteristic of superconductivity in
iron-based materials is that it occurs in the vicinity of {\it two} other
instabilities. Apart from a tendency towards magnetic order, these Fe-based
systems have a propensity for nematic ordering: a lowering of the rotational
symmetry while time-reversal invariance is preserved. Setting the stage for
superconductivity, it is heavily debated whether the nematic symmetry breaking
is driven by lattice, orbital or spin degrees of freedom. Here we report a very
clear splitting of NMR resonance lines in FeSe at $T_{nem}$ = 91K, far above
superconducting $T_c$ of 9.3 K. The splitting occurs for magnetic fields
perpendicular to the Fe-planes and has the temperature dependence of a
Landau-type order-parameter. Spin-lattice relaxation rates are not affected at
$T_{nem}$, which unequivocally establishes orbital degrees of freedom as
driving the nematic order. We demonstrate that superconductivity competes with
the emerging nematicity.
