Engineers, stern, revealing limit (8)
I believe the answer is:
restrict
'limit' is the definition.
(I know that limit can be written as restrict)
'engineers stern' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'stern' becomes 'strict' (synonyms).
're'+'strict'='RESTRICT'
'revealing' is the link.
(Other definitions for restrict that I've seen before include "Keep within bounds" , "Limit, control" , "Keep under control" , "Place limit on" , "hamper" .)