Partly misunderstands star (3)
I believe the answer is:
sun
'star' is the definition.
(the Sun is a star)
'partly misunderstands' is the wordplay.
'partly' indicates a hidden word (part of the clue is used).
'SUN' can be found hidden inside 'misunderstands'.
(Other definitions for sun that I've seen before include "Shiny" , "Nearest star to Earth" , "Warmer" , "It's sol in Latin" , "Bask" .)