Engineers regularly raised limit (4)
I believe the answer is:
rein
'limit' is the definition.
(reining is a kind of limiting)
'engineers regularly raised' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'raised' is a reversal indicator.
The alternating letters of 'engineers' are 'nier'.
'nier' backwards is 'REIN'.
(Other definitions for rein that I've seen before include "Long strap to restrain" , "Restriction" , "Restraint; strap attached to horse's bit" , "Strap to control horse" , "Free ... is carte blanche" .)