Siam revised objectives (4)
I believe the answer is:
aims
'objectives' is the definition.
('aim' can be a synonym of 'objective')
'siam revised' is the wordplay.
'revised' indicates anagramming the letters.
'siam' with letters rearranged gives 'AIMS'.
(Other definitions for aims that I've seen before include "Proposes or intends" , "Sets sight on, having ambitions" , "Purposes or intentions" , "Targets and ambitions" , "objects" .)