Engineers have couple to fix (6)
I believe the answer is:
repair
'fix' is the definition.
('repair' can be a synonym of 'fix')
'engineers have couple' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'have' says to put letters next to each other.
'couple' becomes 'pair' ('pair' can be a synonym of 'couple'**).
're'+'pair'='REPAIR'
'to' is the link.
(Other definitions for repair that I've seen before include "Make one's way (to); fix" , "Travel or proceed toward some place" , "retire" , "Fix, mend" , "It may be effected by" .)