Regular signal to stop reversing through airport (7)
I believe the answer is:
orderly
'regular' is the definition.
(similar in meaning)
'signal to stop reversing through airport' is the wordplay.
'signal to stop' becomes 'red' (traffic lights).
'reversing' shows that the letters should be reversed in order.
'through' indicates putting letters inside (inserted letters go through the word).
'airport' becomes 'orly' (French airport).
'red' written backwards gives 'der'.
'der' put within 'orly' is 'ORDERLY'.
(Other definitions for orderly that I've seen before include "Businesslike" , "Well-regulated" , "Methodical; hospital worker" , "Hospital attendant - neat" , "Hospital attendant; well behaved" .)