  We present an inelastic neutron scattering study of the crystal electric
field levels in the intermetallic ferrimagnets RECo$_{5}$ (RE = Nd and Y). In
NdCo$_{5}$, measurements at $5~$K reveal two levels at approximately 28.9 and
52.9 meV. Crystal field calculations including the exchange field
$B_{\textrm{exc}}$ from the Co sites account for both of these, as well as the
spectrum at temperatures above the spin-reorientation transition at $\sim
280$~K. In particular, it is found that both a large hexagonal crystal field
parameter $A_{6}^6\langle r^6 \rangle$ and $B_{\textrm{exc}}$ are required to
reproduce the data, with the latter having a much larger value than that
deduced from previous computational and experimental studies. Our study sheds
light on the delicate interplay of terms in the rare-earth Hamiltonian of
RECo$_5$ systems, and is therefore expected to stimulate further experimental
and computational work on the broader family of rare-earth permanent magnets.
