Appearance of couple heading off (3)
I believe the answer is:
air
'appearance' is the definition.
(thesaurus)
'couple heading off' is the wordplay.
'couple' becomes 'pair' ('pair' can be a synonym of 'couple').
'heading off' means to remove the first letter.
'pair' with its first letter removed is 'AIR'.
'of' is the link.
(Other definitions for air that I've seen before include "Song - atmosphere" , "Ambience" , "Musical composition" , "Simple melody's" , "The earth's atmosphere" .)