Correct uniform for sappers (7)
I believe the answer is:
redress
'correct' is the definition.
(synonyms)
'uniform for sappers' is the wordplay.
'uniform' becomes 'dress' (dress uniform is a kind of uniform).
'for' says to put letters next to each other (I've seen this in other clues).
'sappers' becomes 're' (Royal Engineers).
'dress' put after 're' is 'REDRESS'.
(Other definitions for redress that I've seen before include "Get back into gear" , "set things right" , "Prepare again - satisfaction" , "Put right" , "Correct" .)