Royal Engineers go and come back (6)
I believe the answer is:
return
'come back' is the definition.
('return' can be a synonym of 'come back')
'royal engineers go' is the wordplay.
'royal engineers' becomes 're'.
'go' becomes 'turn' ('turn' can be a synonym of 'go'**).
're'+'turn'='RETURN'
'and' is the link.
(Other definitions for return that I've seen before include "Give or come back" , "hit back?" , "Comeback" , "second half of journey" , "'Come, go or bring back (6)'" .)