Father is brought back by engineers (4)
I believe the answer is:
sire
'father' is the definition.
(I know that father can be written as sire)
'is brought back by engineers' is the wordplay.
'brought back' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'engineers' becomes 're' (Royal Engineers).
'is' backwards is 'si'.
'si'+'re'='SIRE'
(Other definitions for sire that I've seen before include "Make children" , "Old form of address to king - rise to it" , "Bear" , "Ancestor" , "Generator" .)