Try an overdue reform (9)
I believe the answer is:
endeavour
'try' is the definition.
(I know that try can be written as endeavour)
'an overdue reform' is the wordplay.
'reform' indicates anagramming the letters (letters in a new form).
'an'+'overdue'='anoverdue'
'anoverdue' anagrammed gives 'ENDEAVOUR'.
(Other definitions for endeavour that I've seen before include "Try - Captain Cook's vessel" , "Determined effort" , "Try hard; enterprise" , "Determined attempt" , "Undertaking" .)