Polish hero the limit for Caesar? (7)
I believe the answer is:
rubicon
'the limit for caesar?' is the definition.
(Julius Caesar famously crossed the Rubicon river)
'polish hero' is the wordplay.
'polish' becomes 'rub' (polish meaning rub to make shiny).
'hero' becomes 'icon'.
'rub'+'icon'='RUBICON'
(Other definitions for rubicon that I've seen before include "Italy/Gaul boundary" , "No, I curb the fateful river" , "Line fatefully gone over" , "Caesar crossed this river to take irrevocable step" , "cause of conflict when crossed" .)