Wonder as car reverses in distance (7)
I believe the answer is:
miracle
'wonder' is the definition.
(I've seen this in another clue)
'car reverses in distance' is the wordplay.
'reverses' says the letters should be written backwards.
'in' means one lot of letters goes inside another.
'distance' becomes 'mile' (mile is a unit of distance).
'car' in reverse letter order is 'rac'.
'rac' inserted within 'mile' is 'MIRACLE'.
'as' is the link.
(Other definitions for miracle that I've seen before include "Remarkable occurrence" , "Phenomenon" , "Event that appears to break the law of nature" , "Supernatural occurrence" , "Saintly deed" .)