Get prince occasionally to be heroic (4)
I believe the answer is:
epic
'be heroic' is the definition.
(synonyms)
'get prince occasionally' is the wordplay.
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'get'+'prince'='getprince'
The alternate letters of 'getprince' are 'EPIC'.
'to' acts as a link.
(Other definitions for epic that I've seen before include "Marathon" , "Long story telling of a hero's deeds" , "Large-scale" , "Long poem etc" , "Long poem, book, film" .)