Engineers finished their meal (6)
I believe the answer is:
repast
'meal' is the definition.
(repast can mean a meal)
'engineers finished' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'finished' becomes 'past' (I've seen this in another clue).
're'+'past'='REPAST'
'their' acts as a link.
(Other definitions for repast that I've seen before include "Food - tapers (anag)" , "A formal sort of meal" , "Prates about meal" , "Banquet" , "lunch?" .)