  HD66051 is an eclipsing system with an orbital period of about 4.75 d that
exhibits out-of-eclipse variability with the same period. New multicolour
photometric observations confirm the longevity of the secondary variations,
which we interpret as a signature of surface inhomogeneities on one of the
components. Using archival and newly acquired high-resolution spectra, we have
performed a detailed abundance analysis. The primary component is a slowly
rotating late B-type star ($T_{\rm eff} = 12500\pm200$ K; $\log g = 4.0$,
$v\sin i = 27\pm2$ km s$^{-1}$) with a highly peculiar composition reminiscent
of the singular HgMn-related star HD 65949, which seems to be its closest
analogue. Some light elements as He, C, Mg, Al are depleted, while Si and P are
enhanced. Except for Ni, all the iron-group elements, as well as most of the
heavy elements, and in particular the REE elements, are overabundant. The
secondary component was estimated to be a slowly rotating A-type star ($T_{\rm
eff} \sim 8000$ K; $\log g = 4.0$, $v\sin i \sim 18$ km s$^{-1}$). The unique
configuration of HD\,66051 opens up intriguing possibilities for future
research, which might eventually and significantly contribute to the
understanding of such diverse phenomena as atmospheric structure, mass
transfer, magnetic fields, photometric variability and the origin of chemical
anomalies observed in HgMn stars and related objects.
