Celestial object (3)
(Other definitions for sun that I've seen before include "Major star" , "Earth's nearest star" , "British publication" , "Nearest star to Earth" , "It's sol in Latin" .)
'celestial object' is the definition.
(I know this)
This is the entire clue.
(Other definitions for star that I've seen before include "Heavenly body - leading actress?" , "chamber" , "Actor in a principal role" , "Rush" , "Eg, Antares" .)