Leave the extra-terrestrial on the road (4)
I believe the answer is:
stet
'leave' is the definition.
(I've seen this in another clue)
'extra-terrestrial on the road' is the wordplay.
'extra terrestrial' becomes 'et' (abbreviation - like in the famous 1982 movie).
'on' means one lot of letters go next to another.
'the road' becomes 'st'.
'et' after 'st' is 'STET'.
'the' acts as a link.
(Other definitions for stet that I've seen before include "Let it stand (in proofing)" , "leave things as they were" , "'Let it stand, in printing (4)'" , "Notation meaning leave as is, don't alter spelling" , "Notation meaning leave as is, don't change spelling" .)