Sappers triumph and recover (6)
I believe the answer is:
recoup
'recover' is the definition.
(I know that recover can be written as recoup)
'sappers triumph' is the wordplay.
'sappers' becomes 'RE' (Royal Engineers).
'triumph' becomes 'coup' (I've seen this before).
're'+'coup'='RECOUP'
'and' acts as a link.
(Other definitions for recoup that I've seen before include "Get back, say expenses" , "Get back one's losses" , "Get back or recover - say losses" , "recover money" , "Reimburse or compensate" .)