  We argue that tetragonal CuO (T-CuO) has the potential to finally settle
long-standing modelling issues for cuprate physics. We compare the one-hole
quasiparticle (qp) dispersion of T-CuO to that of cuprates, in the framework of
the strongly-correlated ($U_{dd}\rightarrow \infty$) limit of the three-band
Emery model. Unlike in CuO$_2$, magnetic frustration in T-CuO breaks the $C_4$
rotational symmetry and leads to strong deviations from the Zhang-Rice singlet
picture in parts of the reciprocal space. Our results are consistent with
angle-resolved photoemission spectroscopy data but in sharp contradiction to
those of a one-band model previously suggested for them. These differences
identify T-CuO as an ideal material to test a variety of scenarios proposed for
explaining cuprate phenomenology.
