Men in tandem worked for reform (9)
I believe the answer is:
amendment
'for reform' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for amendment that I've seen before include "Alteration made in a formal document" , "change for the better" , "maybe fifth taken by US criminal" , "Correction" , "Corrective treatment" .)