  We present JWST/NIRSpec observations of a highly magnified star candidate at
a photometric redshift of $z_{\mathrm{phot}}\simeq4.8$, previously detected in
JWST/NIRCam imaging of the strong lensing (SL) cluster MACS J0647+7015
($z=0.591$). The spectroscopic observation allows us to precisely measure the
redshift of the host arc at $z_{\mathrm{spec}}=4.758\pm0.004$, and the star's
spectrum displays clear Lyman- and Balmer-breaks commensurate with this
redshift. A fit to the spectrum suggests a B-type super-giant star of surface
temperature $T_{\mathrm{eff,B}}\simeq15000$ K with either a redder F-type
companion ($T_{\mathrm{eff,F}}\simeq6250$K) or significant dust attenuation
($A_V\simeq0.82$) along the line of sight. We also investigate the possibility
that this object is a magnified young globular cluster rather than a single
star. We show that the spectrum is in principle consistent with a star cluster,
which could also accommodate the lack of flux variability between the two
epochs. However, the lack of a counter image and the strong upper limit on the
size of the object from lensing symmetry, $r\lesssim0.5$ pc, could indicate
that this scenario is somewhat less likely -- albeit not completely ruled out
by the current data. The presented spectrum seen at a time when the Universe
was only $\sim1.2$ Gyr old showcases the ability of JWST to study early stars
through extreme lensing.
