Star granted immunity, initially worried (3,5)
I believe the answer is:
red giant
'star' is the definition.
(I know that red giant is a type of star)
'granted immunity initially worried' is the wordplay.
'initially' says to take the initial letters.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
The first letter of 'immunity' is 'i'.
'granted'+'i'='grantedi'
'grantedi' anagrammed gives 'RED GIANT'.
(Other definitions for red giant that I've seen before include "Megastar" , "Large, cool bright star" , "big star" , "Large star nearing the end of its life" , "Huge Communist" .)