About to leave road? Keep in place (4)
I believe the answer is:
stet
'keep in place' is the definition.
The definition suggests a singular noun which matches the answer.
'about to leave road?' is the wordplay.
'about' means one lot of letters goes inside another.
'to leave' becomes 'te' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'road?' becomes 'st'.
'te' going into 'st' is 'STET'.
Can you help me to learn more?
(Other definitions for stet that I've seen before include "Print as is, don't alter spelling" , "indicates second thoughts are not always better" , "Let it stand (on proofs)" , "Instruction to leave spelling as is" , "Direction in printing to cancel a correction or deletion" .)