Attempt an overdue reform (9)
I believe the answer is:
endeavour
'attempt' is the definition.
(I know that attempt can be written as endeavour)
'an overdue reform' is the wordplay.
'reform' indicates an anagram (letters in a new form).
'an'+'overdue'='anoverdue'
'anoverdue' is an anagram of 'ENDEAVOUR'.
(Other definitions for endeavour that I've seen before include "Expenditure of effort" , "Captain Cook's first ship - DCI Morse's first name" , "Determined effort" , "Try to achieve something" , "Try - Cook's ship" .)