Rocky co-stars in Roll (9)
I believe the answer is:
croissant
'roll' is the definition.
(croissant is a kind of roll)
'rocky co-stars in' is the wordplay.
'rocky' indicates anagramming the letters (letters rocked or thrown around).
'co'+'stars'+'in'='costarsin'
'costarsin' anagrammed gives 'CROISSANT'.
(Other definitions for croissant that I've seen before include "that baker turns out" , "French pastry" , "Breakfast pastry" , "Breakfast item" , "Tasty crescent-shaped French bread roll" .)