Seedy soldiers kept in subject to argument (12)
I believe the answer is:
disreputable
'seedy' is the definition.
('disreputable' can be similar in meaning to 'seedy')
'soldiers kept in subject to argument' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'kept in' indicates putting letters inside.
'subject to argument' becomes 'disputable'.
're' placed into 'disputable' is 'DISREPUTABLE'.
(Other definitions for disreputable that I've seen before include "Lacking public estimation" , "Not of decent character" , "Infamous - shabby" , "Dodgy" , "Superb detail (anag) -shady" .)