Respect engineers in holding-off operation (9)
I believe the answer is:
deference
'respect' is the definition.
(I know that respect can be written as deference)
'engineers in holding-off operation' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'in' indicates putting letters inside.
'holding-off operation' becomes 'defence' (holding off an attack).
're' inserted into 'defence' is 'DEFERENCE'.
(Other definitions for deference that I've seen before include "Submission to will of another" , "given respect" , "honour" , "Respect; submission" , "Compliance with another's wishes, polite respect" .)