In conflict with commander this month (7)
I believe the answer is:
against
'in conflict with' is the definition.
(thesaurus)
'commander this month' is the wordplay.
'commander' becomes 'aga' (I've seen this before).
'this month' becomes 'inst' (I've seen this before).
'aga'+'inst'='AGAINST'
(Other definitions for against that I've seen before include "on the other side" , "Not favouring" , "In contrast to; touching" , "antagonistic" , "Anti, touching" .)