Part of the hero, legendarily (4)
I believe the answer is:
role
'part' is the definition.
('role' can be a synonym of 'part')
'of the hero legendarily' is the wordplay.
'of' indicates a hidden word.
'ROLE' can be found hidden inside 'hero legendarily'.
(Other definitions for role that I've seen before include "Duty" , "Part in play, film etc" , "Stage part" , "Part (in drama)" , "Character" .)