  We announce the discovery of pulsations in HD 23642, the only bright
eclipsing system in the Pleiades, based on light curves from the Transiting
Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and
attribute them to delta Scuti pulsations in the secondary component. We find
four l=1 doublets, three of which have frequency splittings consistent with the
rotation rate of the star. The dipole mode amplitude ratios are consistent with
a high stellar inclination angle and the stellar rotation period agrees with
the orbital period. Together, these suggest that the spin axis of the secondary
is aligned with the orbital axis. We also determine precise effective
temperatures and a spectroscopic light ratio, and use the latter to determine
the physical properties of the system alongside the TESS data and published
radial velocities. We measure a distance to the system in agreement with the
Gaia parallax, and an age of 170 +/- 20 Myr based on a comparison to
theoretical stellar evolutionary models.
