Bill to distinguish a hero (7,4)
I believe the answer is:
william tell
'a hero' is the definition.
(I have seen 'Swiss hero ' mean 'william tell' so perhaps 'hero' could also mean 'william tell')
'bill to distinguish' is the wordplay.
'bill' becomes 'william' (Bill is short for William).
'to distinguish' becomes 'tell' (synonyms).
'william'+'tell'='WILLIAM TELL'
(Other definitions for william tell that I've seen before include "Rossini opera" , "legendary hero" , "C Fourteen Swiss archer hero" , "Successfully resisting, he took a bow" , "Fourteenth century Swiss archer" .)