Engineers finished meal (6)
I believe the answer is:
repast
'meal' is the definition.
(synonyms)
'engineers finished' is the wordplay.
'engineers' becomes 're' (abbreviation for Royal Engineers).
'finished' becomes 'past' ().
're'+'past'='REPAST'
(Other definitions for repast that I've seen before include "Feast, meal" , "A meal concerning time gone by" , "Prates about meal" , "A formal sort of meal" , "Banquet" .)