Engineers wrong to answer back (6)
I believe the answer is:
retort
'answer back' is the definition.
(I've seen this before)
'engineers wrong' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'wrong' becomes 'tort' (legal term).
're'+'tort'='RETORT'
'to' is the link.
(Other definitions for retort that I've seen before include "one used in lab" , "Riposte, reply" , "Part of chemist's equipment" , "may be found in lab" , "Alembic; sharp reply" .)